In a brutal conflict in the summer of either 60 or
61 AD approximately 100,000 humans struggled for the control of the
seventeen-year-old Roman Province in southern Britain. The Boudican
uprising saw rebels and Romans march and fight in numbers probably
never seen since, across a land where resources of water, food and
fodder for the huge numbers of men and supporting animals were
crucial determining factors in the outcome. In this essay these
under-appreciated resources, mistakenly perceived as mundane, are
calculated and examined to try to further narrow down the search for
the site of Boudica's last battle.
Napoleon famously said: “An army marches on
its stomach”; he might have said, with equal certitude that:
“An army walks on water”. Sadly for his Grand Army of
c.500,000 marching to Moscow in 1812, which was essentially destroyed
by lack of sustenance, he did not practice what he opined. However,
the Russians did; they withdrew before the vast Napoleonic onslaught,
leaving barrenness in their wake, until the pitiful rump, c.20,000
men of the Emperor’s army, crawled back across the river
Niemen. This story of destruction by logistical weakening contains
In an earlier Empire, Roman army commanders also
understood that a victorious campaign was determined as much by
logistics as by the sword. Hundreds of years of bloody conquest had
created a body of military knowledge and practice that was not
matched until the modern era.
of logistics was used as a weapon by applying it to the enemy's needs
and weaknesses, hence:
follow the same policy toward the enemy as did many doctors when
dealing with physical ailments, namely, that of conquering the foe by
hunger rather than by steel", so cites Frontinus (in Strategemata, VII,1) of Julius Caesar.
strategy regarding the use of logistics as a weapon would not have
been limited to food – the availability of firewood, fodder and
most especially water - would have been understood to control many
aspects of a conflict. Additionally, conquering by the denial of
logistical elements implies that Roman armies were structured to be
immune from the same stratagem. In this essay these factors will be
measured, calculated and applied to the deadly struggle between
empire builders and the emancipator of tribal rebels.
Readers unfamiliar with the story of the Boudican
rebellion, or the author's earlier amalgam of terrain analysis
techniques, known archaeology and the written accounts, are invited
to read www.britarch.ac.uk/ba/ba114/feat3.shtml or go to the Boudica: Terrain Analysis page. The former is an article published in British Archaeology (but now
without images and maps) and the latter a longer version with maps.
1: Location map. Significant roads are colour highlighted. Please
note that not all the roads depicted would have existed at the time
of the rebellion. Elements of this image are ©
Crown Copyright. All rights reserved 2013.
Review of Events
A précis of events
in 60/61AD, based on Tacitus, would mention that Caius Suetonius
Paulinus was the Roman Governor in Britain who commanded the 2nd,
9th, 14th and 20th Legions, together
with an unknown number of auxiliary and cavalry units, and that he
was interrupted in his conquest of the Druidic stronghold on Anglesey
by news of a rebellion by the Iceni, a tribe in modern East Anglia
led by Boudica, a woman driven by revenge for grievous slights by
Roman oppressors. The Iceni, together with other local allies,
including the Trinovantes located in modern Essex, stormed and
destroyed Colchester, the principle Roman town in Britain. Meanwhile,
the veteran cohorts of the 9th Legion, led by their commander Petillius Cerialis, marched
from their fort (probably Longthorpe near Peterborough) to suppress
the revolt and possibly to save the Romans in Colchester but were met
en route, at an unknown location, by the already victorious Britons.
The veteran infantry of the 9th Legion were destroyed and
Cerialis retreated, with his surviving cavalry, back to their fort.
This news would probably
have reached Suetonius as he marched from Anglesey towards London
with cohorts and auxiliaries from the 14th and the
veterans of the 20th Legions who numbered, according to
Tacitus, 10,000 armed men. This bad news would be more than doubled
when Suetonius heard that the 2nd Legion, probably based
in Exeter, was not marching to join him as he had ordered. Suddenly,
Suetonius had lost something approaching half of his effective combat
strength; he was marching the 14th and 20th Legions through hostile territory towards London and faced the
possibility of meeting a horde of Britons, possibly numbering in the
hundreds of thousands. On reaching London he decided to abandon the
proto-city and marched his men, plus any civilians who could keep up,
away from the Britons who were about to destroy the town.
A less destructive fate
befell St. Albans to the north of London. The horde of Britons
followed Suetonius as he attempted to march away from the greatest
danger to his army but circumstances forced him to offer battle. The
Roman legionaries, auxiliaries and cavalrymen were victorious,
apparently killing tens of thousands of Britons for little loss.
Summary of the earlier terrain analysis work
The author's earlier
analysis of terrain, and how this limits the location of possible
battle sites, coupled with Tacitus' written account, was explained in
the documents referenced above.
In summary, once
Suetonius had arrived in London with his army he was no longer the
prospective destroyer of the rebellion, but a surprised fugitive from
Boudican revenge and annihilation. Suetonius had to choose the
direction of march out of London; for various reasons (Fig.14) it was
concluded that he marched westwards, towards Silchester, using the
shortest and quickest route to the Fosse Way and safety in the camps
at either Cirencester, Gloucester, or even Exeter. It is possible he
had an alternate strategy, namely joining forces with the missing 2nd Legion and giving battle.
This earlier work
speculated that, for whatever reasons – Tacitus does not
explain - Suetonius turned and gave battle somewhere within, or close
to, the Kennet river valley.
Logistics of the Roman army
After the reforms of Gaius Marius, c. 100BC, the
Roman army became professionalised: soldiers from all classes
enlisted for decades; equipment was largely standardized; huge and
slow moving baggage trains were reduced, and individual soldiers were
trained to carry much of their armour, equipment and food.
Roman legions could now march for 29km each day (as
a comparison the US Army marches 20-32km/day), with bursts of
forced-marching if required, and may have been capable of
approximately 22 days of independent operation before additional
supplies were needed. These figures are based on the use of a troop
baggage train, essentially mules closely associated with each unit,
rather than an army baggage train. The latter would have been larger,
made use of wagons and mules, carried more supplies and heavy
weapons, was slower and would have supported the whole army, not just
individual fighting units as did the troop train. The troop baggage
train is selected as the primary transport unit in this essay because
it is thought likely that the army baggage train would have remained
with the fighting units left behind in North Wales and Anglesey,
while Suetonius, and units of the 14th and 20th Legions, moved rapidly south along Watling Street to London.
To place the 22 days of operation into the Boudican
context it can be calculated that this would allow the legionaries to
march 638km at 29km/day – enough to travel the 540km from
Anglesey to London, then onwards to Silchester, Cirencester and
finally Gloucester, and leave 3-4 rest days, i.e. roughly one in
five. However, we have no evidence that Suetonius' legionaries and
mules did have this capacity, but the figures are illustrative of the
capabilities of the legions, and suggest that, allowing for foraging
and requisitioning from local forts and London merchant-warehouses,
that Suetonius probably had little difficulty feeding his men during
the campaign. Of course the actual marching rate during the Boudican
campaign would have been variable, for example falling lower than
29km/day when harassed by rebels, but attempting to match this
variability to recorded events is fraught with uncertainties and,
ultimately, pointless. Nevertheless, as we shall discuss, the Roman
army will be shown to have been the significantly quicker unit of the
The core unit of a legion was the eight man contubernium which shared a single tent, probably one servant,
or slave, and two mules. The servants cared for the general needs of
the legionaries, fetched water, cooked, cared for the mules and were
an essential and integral element in the effectiveness of the eight
man fighting unit. Each legionary carried all his clothing, armour,
weapons, sundry essential items (such as a sickle) and could carry
rations for 17 days. The total weight came to 43.4kg; in comparison,
British army soldiers during the 1982 Falklands conflict typically
carried 54kg, while US Army riflemen in Afghanistan regularly
carried 40 to 58kg. The Roman mules carried shared, larger and
heavier units of equipment such as the tent and cooking pots,
together with their own fodder and additional food stuffs for the
men. Crucially the mules were fast and rugged enough to match the
pace of the trained legionaries, and did not lag behind the marching
units, or slow them down.
It is estimated that a Roman
era mule could carry 135kgs. The two mules could carry 145kgs
of non-food stuffs (tents and the like) and at least 17 days, or
38.5kgs, of mule-grain. The remaining mule capacity of 86.5kgs could
be taken up with five more days of legionary and mule-grain –
hence the figure of approximately 22 days of independent operation by
Historical accounts state that the marching legions
supplemented their carried-rations with food acquired by purchase,
requisition, foraging and pillaging, the method being determined by
varying circumstances. Foraging was essential to the maintenance of
the marching units, especially for firewood, water and fodder, and
was conducted in a daily, disciplined and practised manner.
Fodder was the main staple for the mules and horses;
the animals could be released to pasture and/or the legionaries would
use their sickles to gather fodder for immediate consumption or later
transport. Roman commanders knew how crucial fodder was to any
campaign; for this reason they would delay their marches until the
grass-growing season and retire to winter quarters once fodder was
insufficient. The importance of gathering fodder is further
emphasised by each legionary carrying a sickle, although it was also
used for harvesting grain.
It is also thought that each legionary carried a saw
for the gathering of firewood, another crucial requirement of the
marching legion. Without fire wholesome meals could not be prepared,
wet men would become sick, spirits and morale would fall and could
lead to a general feeling of wretchedness.
The water needs of the marching legionary
An adequate water supply was essential for the well-being, independent
efficiency and effectiveness of the legions. Furthermore, Jonathon P. Roth, in his excellent: 'The Logistics of the
Roman Army at war (264 B.C. - A.D. 235)', states that: “Caesar measured his
marches and set up his camps in order to assure an adequate water
Estimating the water requirements of the marching man is notoriously
difficult today; even more so for a Roman legionary. Although there a
number of statements in the historical texts concerning the amount of
water consumed by a legionary, none are thought to be sound,
certainly not empirical, and cannot be relied upon. Consequently the
scientifically sound studies of the water consumed by modern
soldiers, conducted by the medics and professionals of the modern US
Army, were examined for this study: this empirical data is,
therefore, a proxy for the water required by a legionary.
2 is of a graph of the water needs of US Army soldiers operating
under varying climatic conditions and at varying work-rates. The
work-rates are calibrated to energy expenditure, such that a
sedentary soldier expends 2,500 kilocalories a day (kcal/day) –
the lower purple band in Figure 2 – while a hard-working
soldier expends 5,000 kcal/day – the blue band. The average
work-rate for all measured US Army, US Marine and Israeli personnel
is 4400 kcal/day.
of Suetonius' legionaries marched at 29km/day, carried approximately
43kg of clothing, equipment, arms, armour and food, and before
night-fall helped build a marching camp which he then took his turn
to guard. He had probably repeated this labour since the start of the
campaign to suppress the Druids in Anglesey in the early Spring, and
continued to do so as he marched from that island to London and then
on to a battle site; a distance in excess of 400km.
2: Estimates of daily water needs for a range of environmental
conditions and energy expenditures. From:
S.J.Montain and M.Ely, Water Requirements and Soldier Hydration,
Borden Institute Monograph Series. Primary data source: Sawka
MN, Wenger CB, Montain SJ, et al. Heat Stress Control and Heat
Casualty Management. Washington, DC: Headquarters, US Department of
the Army and Air Force; 2003: 13. TB MED 507/AFPAM 48-152.WBGT:
wet-bulb globe temperature.
Tacitus tells us that Suetonius marched to London: “amidst
a hostile population to Londinium”, an observation that
indicates that legionaries were probably also defending themselves
against skirmishing tribesmen. All-in-all, it seems reasonable to
assume that the legionary was expending a considerable amount of
energy over a protracted period of time, and at the height of Summer.
Therefore, it is estimated that the legionary would
probably have expended at least 4,500kcal/day while marching which,
at a temperature of 25C, gives a daily, total water requirement of 10
US quarts or 9.46353 litres/legionary/day. However,
this figure may be too high for a Roman legionary, a shorter,
lower-weight, hardier and more rigorously-trained individual than the
modern equivalent. Hence, in this essay a figure of 9 litres per day
has been estimated as reasonable. It should be borne in mind that
this is a conservative measure: the energy expenditure may well have
exceed 4,500kcal/day, and does not include additional water required
for cooking, washing, cleaning clothes etc..
The raw statistics, discussed in this and the
preceding section, clearly show how vital the management of logistics
was to the Roman army. It allowed the Romans to deploy an
independent, self-sufficient, self-sustaining, rapidly-moving,
well-trained fighting force into the field for weeks at a time. It is
difficult to assign these attributes to the Boudican rebels –
probably an ill-disciplined and ill-prepared, amorphous mass of
tribal warriors, youths, agricultural workers and their followers.
Logistics of the Boudican rebels
It is important to make clear at the outset that
there is no firm evidence of the Boudican rebels management of
logistical supply. However, it is known from Tacitus' account, that
the rebel force included an unknown number of wagons filled with
supporters and wives. This seems to follow common European tribal
tradition and may be, in part, related to summer travel to religious
and trading sites. Therefore it seems reasonable to assume that
'camping equipment', and food and fodder was transported for the
warriors in the wagons. There were probably transportation mules and
donkeys, but assigning numbers is difficult. Wagons drawn by oxen
were probably common, but these beasts move slowly, typically only
2km/hour for a maximum of six hours/day; a substantial limiting
factor on the speed of march. The Iceni, Boudica's tribe, seem to
have favoured horses; they appear on their coins, and might have been
used in large numbers as transport, but probably not as cavalry in
the strictest sense – the majority of warriors might have
ridden to battle, either in chariots, or mounted, and then fought
dismounted. Elite warriors may have used their chariots as ancient
tanks, or weapon platforms, but they would have been relatively few
in number. These may have been common traits amongst the tribes of
Eastern England and elsewhere.
Preparing for a campaign, or raid, probably amounted
to gathering as much food etc. as could be spared from the home, farm
or village, and supplementing this by foraging and pillaging as the
warfare progressed. Centrally-controlled and managed foraging, or
food-sharing, was probably minimal. Tacitus tells us that the
tribesmen bypassed defended places but violently plundered other
habitations. Stealing valuable, or otherwise desirable, objects was
probably one motive for this activity, but acquiring foodstuffs and
fodder and transporting it back to the wagon train to feed the mass
of the tribal horde was just as important. One consequence of this
sort of raiding activity is the spreading of tribal forces across a
large area. There may have been a compact mass of travelling people,
wagons and animals directly following the Romans out of London, but
many fast-moving younger warriors would have travelled far, not least
for reconnaissance and harassing purposes. In contrast, the Roman
system held all units in close proximity, except possibly for cavalry
sent to screen the main army, or on reconnaissance.
The tribal practice of extracting supplies from the
local population, towns and farms would work well for short raids in
the more agriculturally-rich lowlands of southern Britain. However,
it would pose considerable provisioning difficulties if attempted in
the harsher, drier, less populated chalk and limestone uplands of the
same region. The water-poor uplands would have supported pastoral
agriculture - raising sheep, cattle, goats, and horses - with arable
cultivation being possible only in the narrow river valleys where
most settlements occurred. Of course, finding enough fodder or
grazing land for transport animals might not have been too
problematic (assuming the Romans did not scorch the earth). However,
finding sufficient food for the tribal horde would have posed great
difficulties. Firstly, the thin, high river valleys had little area
for growing crops; secondly, the locals, being few in number, would
not have grown much beyond their own needs; thirdly, what food was
available in quantity was also mobile – the grazing animals
would probably have been driven away from the horde, as they probably
had been for millennia; fourthly, although we have no evidence,
written or otherwise, it is possible that the retreating Romans used
a scorched earth policy, using the prevailing eastward blowing winds
to burn settlements, fodder and crops. In this case the Romans would
have continually moved into fresh land while the rebels marched
consistently into a scourged landscape. The overall result of moving
from the rich lowlands to the poor uplands, might have been a forced
concentration of the Boudican horde into the river valleys as it
sought water, and probably acute strain as food supplies ran down or
Figure 3: geographical areas of Southern Britain. Elements
of this image are © Crown Copyright. All rights reserved 2013.
The mixed use of mules, horses and oxen for
transport, coupled with the need to forage or pillage to feed the
assembled rebel horde, probably reduced the marching rate to 16km per
day. This figure is thought to be the mean during the Mediaeval
period when armies used similar transport means and food gathering
tactics, and is probably a reasonable one for the Boudican rebels.
This is not to suggest that there were not fast-moving rebel units
capable of matching the Roman army. Nevertheless, there are at least
two consequences of this slow marching rate: firstly, the Roman army
on leaving London, and assuming a westwards-march using the road
system, could have consistently outpaced the horde by approximately
13km per day; secondly, the horde following the Roman army, and
entering the chalk uplands beyond Silchester, would have taken
between four and six days to clear the uplands. However, in following
the Romans, who would only have taken three to four days to cross the
chalk uplands, the rebels would have entered a land probably depleted
of food-stuffs, where nearby fodder had already been consumed or
destroyed, and where the water supply would be diminished and
probably polluted. The stress imposed upon the rebel horde by these
factors might have caused enough strain to slow it even further which
would compound the stress. Additionally, if the rebels had not been
able to replenish their food supplies since leaving their homelands,
possibly because the Romans had either consumed or destroyed it in
London and elsewhere, then starvation may have been evident, or at
least a possibility, severely damaging morale, fighting effectiveness
and possibly causing some tribesmen to abandon their cause.
In conclusion, the crucial point is that the Romans
could sustain their forces in the field for weeks, including within
the relatively water-, food- and fodder-poor regions, such as the
Chilterns, Cotswolds, White Horse Hills, Salisbury Plain and the
Weald (Figure 3): the Boudican rebels could not.
Roman and British water requirements
Attempting to place firm numbers on the amount of
foodstuffs, fodder and firewood required by the two combatant groups
is very difficult and open to inaccuracies in the amount available
and consumed. However, as we have already discussed, in the 20th and 21st centuries military authorities have measured the
water requirements of soldiers to enable adequate logistical support.
In addition, hydrologists in Britain and elsewhere have extended
great efforts to measure the available water in catchments and
rivers. This modern knowledge can be retrofitted to the situation in
60/61AD, enabling the assessment of available and consumed water, and
how these parameters may have influenced the outcome of the revolt.
The situation and the number of combatants is described by Tacitus
writing in c.109AD. Tacitus was the son-in-law of Agricola who was
serving in Britain as a tribune at the time of the uprising; he may
have been present at the final battle. The author takes Tacitus'
numbers of combatants at face-value: better to accept 1st century AD inaccuracies or political spin, than to introduce
additional 21st century AD unsubstantiated bias.
In the remainder of this section we will make an
assessment of the water requirements of the combatants before
examining the hydrology of southern Britain in the following section.
Numbers of >
Unit total litres
Total army litres/day
Total army cubic metre/day
Minimum river flow cubic metre per second
Minimum river flow (daylight corrected)
Total for army per day
290.63 cubic metres
Table 1: Roman Army Water Requirement.
Table 1 is an
estimate of the water requirements for the soldiers, servants and
slaves, mules and horses in Suetonius' army. They are based on
generally accepted numbers for Legionary forces, specifically the
legionary cohort system of the early Roman Empire of the 1st and 2nd centuries AD. There is no attempt to vary these legionary numbers due
to the presence of auxiliary soldiers, siege equipment or additional
cavalry units, beyond those cavalry normally assigned to a legion. In
emphasis therefore, the number of soldiers etc. in Table 1 is
anchored on the generally accepted legionary standard of:
basic unit of 8 soldiers (contubernium),
a centuria consisting of 10 contubernium = 80 soldiers,
a cohors consisting of 6 centuria = 480 soldiers,
legion consisting of 9 cohors of 480 soldiers and one 1st cohors of 800 soldiers = 5120 soldiers.
Each contubernium was supported by at least two servants and the same number of mules
used as baggage transport. Typically 120 cavalry are attributed to a
legion, but in this study this is doubled to reflect the probable
presence of at least one remount; there may have been more. It should
be stated that these numbers exclude officers, their servants and
The figure of 10,000 soldiers in Table 1 is taken
from Tacitus. The 2,500 number for citizens is the author's estimate
based on the evacuation of London, Romano-British refugees joining
the army as it marched, and possibly large numbers of friendly
Britons, e.g. Atrebates, also seeking shelter.
These figures are considered to be reasonable,
probably an under-estimate, and based on the supposition that the
main army baggage train was left behind in North Wales. Figures for
the water needs of animals, working hard either marching and/or
carrying loads in a temperate climate in summer, are taken from a
number of sources.
In the lower half of Table 1 are figures for the
total water requirement of the Roman army expressed in a number of
units. Each day the army required a total of 290,625 litres, or
290.63 cubic metres. To satisfy this need the rivers or streams the
army was extracting from would need a minimum flow, in each 24 hour
period, of 0.00336 cumec (cubic metre per second – i.e. the
volume of water, passing through a river cross-section in one
second). However, it would of course have been extremely dangerous
and foolish to extract water after nightfall, therefore, in the final
column of Table 1, the 24 hour figure is adjusted for the number of
daylight hours in August to give 0.00447 cumec.
However, the figure of 0.00447 cumec is the minimum required by Suetonius' army; it is probably not the amount a Roman
army surveyor would have in mind when selecting a suitable river to
satisfy the demand of a marching camp or army prior to battle. To
discover that amount we must turn to an examination of Roman marching
Roman armies always occupied a marching camp at
night. Either the camp was newly built, or an old one re-used, often
with suitable modification based on the number of new occupiers. The
camps may have been used for days or weeks at a time, especially when
the Roman army was campaigning, and not at always by the same unit.
The author has written another essay which fully
describes the method used to examine 374 known marching camps
in Britain and the use they can be put to predict unknown camp locations. This essay can be found at:
For our immediate purpose of estimating the amount
of water the surveyor might have thought suitable we can extract
Figure 4 from that essay.
Figure 4: Plot of the percentage difference, or excess, between the demand
and supply. 307 marching camps displayed within colour coded Groups.
See text for further details. River flow rate calculations are for
August. Log scale on both axes. Elements
of this image are © Crown Copyright. All rights reserved 2013.
This image shows for each
of 307 marching camps the percentage difference, or excess, in August
between the supply (flow-rate of rivers) and the demand (water
requirement for the force occupying the camp). One of the striking
details is the base line (red) which marks the 10% excess mark on the
Y axis, i.e. only 5 or 1.63% of the 307 camps, are situated below the
10% excess line. Conversely, and stating the obvious for emphasis,
98.37% of all camps had rivers that supplied an excess greater than
10% of what was demanded. It is thought unlikely that the Roman camp
surveyor would have thought that a 10% excess was sufficient, and for
that reason, it is postulated that surveyors chose as a minimum
rivers that could supply twice as much water as was demanded, i.e.
the 100% excess mark on the Y axis, Figure 4.
Therefore, the minimum
river flow figure from Table 1 of 0.00447 cumec should be doubled to
0.0089 cumec; it is this figure that has been used to determine which
of the rivers across Britain could have sustained Suetonius' army,
both as it marched and as it camped prior to battle.
Oxen, horses and mules
Numbers of >
Unit total litres
Total army litres/day
Total army cubic metre/day
Minimum river flow cubic metre per second
Minimum river flow (daylight corrected)
Total for army per day
2,220 cubic metres
Table 2: Boudican Rebels water requirement.
Turning to the Boudican rebel force, Table 2
displays, in the same manner as that for the Romans, estimated and
calculated figures of water consumption. The final figure, of 0.03417
cumec of minimum river flow adjusted for daylight is, self-evidently,
a result of the larger numbers of humans and animals marching in the
To be consistent these figures require an
explanation. The Roman army figures are rooted on the figure of
'10,000 armed men' given by Tacitus, an author not given, experts
contend, to much exaggeration, embellishment or theatrical posturing
(some would say in contrast to Cassius Dio, who also gave an account
of the Boudican rebellion). Similarly, the figures in Table 2 are
rooted in Tacitus' account when he claims 80,000 rebels were killed
in the final battle. Tacitus states that women were also killed:
presumably these were on the wagons supporting the warriors. One can
find speculative methods to parse Tacitus' figures in a number of
ways, but this author supposes that the simplest approach is to
accept his figures. Therefore, this study divides the 80,000 figure
into 60,000 warriors, supported by 20,000 women, and sundry other
non-combatants. Of course, not all defeated attendees at a battle
die: many escape or become captured and later sold into slavery. This
study does not estimate the number of such survivors. The figure of
25,000 animals includes horses, mules, donkeys and oxen: it is an
estimate based on a third used as mounts, the rest as pack-animals
and hauling the rebel wagon train. Like the figures for rebel humans,
it is probably too low, rather than too high. In summary, the rebel
numbers are based on Tacitus' figures, exclude the body of survivors
and may be too low.
The result is that the rebels needed 0.03417 cumec
(Table 2), but if they were following Suteonius along a single river
course then supply increases to a minimum of 0.04 cumec (rounded
down) – a whole order greater than Suetonius' needs.
The Hydrology of Britain
Southern Britain, the operational region for the
Boudican revolt, can be generalised as a small, low-elevation
landmass with commensurate drainage basins and rivers. The general
consequence is of many rivers and streams with relatively small flows
in comparison to those in Europe. For decades the hydrologists at the
Centre for Ecology and Hydrology (CEH, formerly the Institute of
Hydrology, Wallingford) have measured, calculated and attempted to
produce models to predict the flow within rivers. Of late, much
effort has been made to understand and model low flows, usually by
statistical inference based on measured gauged values and catchment
parameters, which has produced a number of key papers of the methods
employed – it is these that have been utilised within this
study to produce the values and maps depicted.
5: The rivers of Britain greater or equal to 0.05 cumec of flow as
calculated for this study. Inset: Rivers and streams of the Kennet
river catchment (calculated lower-order streams and rivers shown).
In outline, the catchment water balance methodology
was used in this study for the whole of Britain (Figure 5). This
involves calculating the mean flow in rivers by use of rainfall,
potential evapotranspiration losses, and catchment characteristics
such as area sizes, topographic and geological descriptors and models
of the river systems. All these investigations, and other supporting
statistical and mathematical calculations, were conducted within SAGA
(System for Automated Geoscientific Analyses),
a GIS and calculation engine, that contains the key hydrological
modules used in this study.
We are interested in river flows in the summer of
60/61AD, especially those within and on the margins of the chalk and
limestone uplands of southern Britain. Therefore, the values of the
Q95, for the period 1961-2006, have been computed for August and for
naturalised catchment and river systems. Essentially these Q95 values
- at the height of summer, when rainfall, surface runoff, aquifer
discharge and consequently river flows are at a minimum, tells
us where these large armies could march and give battle.
It should be made clear that the calculation of low
flows is fraught with difficulties and uncertainties, especially when
examining flows in the ranges required for this study. The results
are imperfect, have unknown error ranges, but are generally
representative of the flows the protagonists would have experienced
in marching across southern Britain.
It is in part due to these hydrological
uncertainties that the numbers of humans and animals was kept low,
and the water requirement for humans lowered to 9 litres/man/day
rather than use the larger figure from the investigations of the US
The base data used in the for-mentioned calculations
Radar Topography Mission (SRTM), Jarvis A., H.I. Reuter, A. Nelson, E. Guevara, 2006,
Hole-filled seamless SRTM data V3, International Centre for Tropical
Agriculture (CIAT), available from http://srtm.csi.cgiar.org
long term average per month for years 1961-2006 from the
Meteorological Office - http://www.metoffice.gov.uk/climatechange/science/monitoring/ukcp09/download/longterm/fivekm_monthly.html
figures from MODIS 16; a NASA/EOS project to estimate global
terrestrial evapotranspiration from the earth land surface by using
satellite remote sensing data. http://www.ntsg.umt.edu/project/MOD16/
6: Comparison of Q95 flow values from this study with those of the
Centre for Ecology and Hydrology (CEH). See text immediately below
for description. Elements of this figure are the copyright of the Natural Environment Research Council (NERC). All rights
Due to the uncertainties resulting from the method
it was thought prudent to compare this study's results with those of
The CEH publishes 21 naturalised values of Q95
(Figure 6, table on the right) at various gauging stations across the
UK and these were correlated with the equivalent values from this
study (Figure 6, top graph). The linear regression line gives a coefficient of determination (R squared) of 0.86, a high “goodness of fit” value. The
lower graph is of all 1,392 Q95 CEH gauge station values throughout
the UK correlated with this study's values; the coefficient
of determination is 0.67, a fairly high level of “goodness
of fit” considering that only 21 of the CEH stations are
naturalised compared to all of them for this study.
Figure 5 shows the river systems calculated within
SAGA and used as a base for all other calculations and river
displays. Figure 7 shows the same river system but with the removal
of all channel sections with flows less than that required by the
Romans (0.0089 cumec at the minimum). This clipping action removes
many sections, especially those in the chalk and limestone uplands
Figure 8 represents the minimal water available to
the Boudican horde as it followed the Roman army. Here the base river
system (Figure 5) is limited to 0.04 cumec which produces a dramatic
reduction in the number of river sections available to the horde,
essentially to those of the major rivers and their main tributaries.
The difference between Figures 7, rivers capable of supplying the
Romans, and 8 is stark, and clearly shows how constrained the horde
might have been by its need for adequate water.
History relates that the Romans left London, marched
for some days, and then offered battle. The tribal leaders would have
known that their only chance of a successful rebellion was to destroy
Suetonius' Roman army in the field, before tackling the legionary
forts. Consequently the main rebel force had to follow Suetonius as
he marched away from London and therefore had to contend with damaged
river systems already depleted and probably polluted. Similarly, any
wells would have been rendered unusable, either by Roman consumption
or deliberate act. As we have already discussed, food stuffs and
fodder would probably have suffered similarly.
7: River channels with minimum water flow required by the Roman army
(0.0089 cumec). Yellow dots are the 110 possible battle sites from
8: River channels with the minimum water required by the rebels
following the Romans (0.04 cumec). Yellow dots are the 110 possible
battle sites from this study.
8 suggests that the vast numbers of rebels, with their slow moving
(16km/day) wagon train, would have tried to remain adjacent to the
main rivers of southern England. The horde's natural tendency might
have been to remain within the river valleys and off the Roman roads,
but that would have slowed the main body even further. Consequently,
the tribal leaders would probably have enforced the need to move as
quickly as possible, to stay close to Suetonius, and to follow using
the Roman road system. However, that system was built to serve
well-organised, legionary units (typically 1000s of men), not a huge
horde of ill-disciplined tribesmen numbering tens of thousands. The
combination of the demand to follow the Roman road system, together
with a high water replenishment rate, created a situation even more
unfavourable to the advancing horde.
leaving London before the horde arrived, Suetonius might have
realised that he was not only withdrawing, but also gaining a
strategic advantage: his was the choice of the direction of march; he
could lead the rebels where he wished and in doing so, place them at
a logistical disadvantage.
of the powerful attributes of a GIS system, such as SAGA, is its
ability to extract multiple datasets from different layers, determine
some new variable and display the results in another layer. In this
section the data layers to be acted upon were the Roman road system
(Figure 1) and its conjunction with rivers of sufficient water
quantity for the Romans and rebels (Figures 7 and 8). The result is a
series of maps showing points where the protagonists could replenish
their water to meet minimum needs along their line of march.
is important to re-emphasise that not all the Roman roads shown in
the following images would have existed in 60 or 61AD.
Roman replenishment map is shown as Figure 9, where the intersections
of the roads with a river that could supply the minimum need (0.0089
cumec), are shown as green blocks.
9: The Roman army replenishment map. The green areas are
locations on the road system (maroon strings) that intersect rivers
(blue strings) capable of supplying the minimum water required
(0.0089 cumec). Background is of the general topography. Elements of
this image are © Crown Copyright. All rights reserved 2013.
distribution of Roman replenishment sites is such that nearly all
sections of road could have been be traversed within one day (at
approx. 29km/day) and also have minimally adequate water at both ends
of the section: this is a result of design.
aspect of Roman road engineering is displayed in Figure 10 along the
route known as the Portway between London and Silchester. The road
must cross the Thames at some point and this is achieved at Staines
where the river is thought to have been crossed by a Roman causeway
and bridges – hence the Roman name of Ad Pontes – 'at
the bridges'. Multiple bridges might have been required to not only
cross the Thames, but also the river Coln which joins the Thames in
this location. The road is not well-located directly west of Staines
but is thought to arrive at Virginia Water after 6.5km. At this point
Suetonius would find sufficient water for his army but thereafter,
for a distance of approx. 24km, is a section of road without adequate
water until the river Blackwater is reached south of Farley Hill. The
approximate distance between Staines and the Blackwater is 30km,
close to the standard legionary marching rate of 29km/day: as
elsewhere on the Roman road system, the marching day rate was
apparently matched to night-stops with adequate water.
10: The Portway between Staines and Silchester (maroon). Rivers shown
(blue) can supply 0.04 cumec, sufficient for the Boudican horde.
Purple coloured areas are Roman replenishment sites; the same for the
horde in green. Elements of this image are © Crown Copyright.
All rights reserved 2013.
postulated deliberate routing of roads to provide water is possibly
demonstrated by another feature of the Portway between Virginia Water
and Silchester: the kink in the road north of Bagshot. There is no
topographical reason why the road should take this route, which
extends the distance between Virginia Water and Silchester, but an
hydrological one does exist, i.e. the kink is located at its junction
with the headwaters of the Windle Brook and its tributaries. Here
Suetonius would find insufficient water but there would have been
enough for smaller marching units and civilian traders, and enough to
slake the thirst of Suetonius' legionaries.
principal points of this example (Figure 10) are that the Roman road
engineers' design allowed for not only the rapid covering of
distances, but also ensured there was an adequate water supply at
to the story of the uprising, Figure 10 shows that the Boudican horde
would not have found sufficient water along the road between Staines
and Farley Hill, a distance of approximately 30km, or a march of two
days, but without sufficient water.
one might expect, Figure 9 shows that for most of the road system
water supply would have been adequate, with only a few stretches
across the high chalk and limestone regions, e.g. Salisbury Plain,
the Cotswolds and the chalk downs north of the Kennet river valley,
causing some concern for a lack of water. However, this would have
been mitigated by the knowledge that legionaries were trained and
disciplined in the use of water-skins and possibly amphorae (or
similar) transported on mules. Keeping the men adequately hydrated
was very important, equally so the mules and horses of the army: no
transportation equates to no provisioned march, and all that that
would have entailed.
more could be said about these maps and what it may tell us about the
planning and use of the Roman road system. However, for brevity's
sake, a small and simple example will be given of how water might
have influenced one possibility.
11: A map of Silchester and the local, surrounding rivers/streams. Rivers greater than 0.0089 cumec = blue string: less than 0.0089
cumec = yellow strings. Maroon lines are Roman roads. Green areas are
Roman replenishment points and favourable marching camp areas
adjacent to the road system. The graticule is in metres. Elements of
this image are © Crown Copyright. All rights reserved 2013.
the King of the Atrebates, was an ally of the Romans and probably had
his capital at Silchester, the site of extensive burning and a 20
year building hiatus between 50 and 80AD as reported by Professor
Mike Fulford and his team of archaeologists from Reading University.
The suggestion is that this burning might be attributed to the
Boudican uprising, possibly by the rebel horde as it followed the
Roman army westwards, or even by the Romans using a scorched earth
policy. It is instructive to ask why Silchester could not be defended
by the Romans. The answer lies in two observations. Firstly,
Silchester, although on locally raised terrain, is a poor site for
building defences robust enough to withstand an attack by a large
body of tribesmen. Secondly, as Figure 11 shows, the Romans would
have had an impossible task to defend a perimeter, greater in radius
than 1km, to safeguard sufficient water for themselves if they were
besieged (this ignores the use of polluted wells and small springs,
which are known to exist within Silchester, but would not have
provided enough water for the Roman army and Atrebates). If Suetonius
did rest for the night near Silchester, then the bulk of his army
would probably have camped approx. 1.5km to the east alongside the
river with more than sufficient water for his men and beasts –
the green areas in Figure 11.
12: The Boudican horde replenishment map for the case when it follows
the Roman army. Green areas are locations on the road system
(maroon strings) that intersect rivers (blue strings) capable of
supplying the minimum water required (0.04 cumec). Background is of
the general topography. Elements of this image are © Crown
Copyright. All rights reserved 2013.
replenishment map for the Boudican horde (Figure 12) is far more
sparsely populated with green replenishment areas than the Roman
equivalent (Figure 9) – an unsurprising result given the
difference in water required, i.e. 0.04 versus 0.0089 cumec,
respectively. Once the horde had left the Thames river basin - the
area bounded by the Chilterns, the chalk uplands of Salisbury Plain
and White Horse Hills, and the North Downs (Figure 2) – its
water-strain increased significantly. Of course, the rebels could
have moved off the Roman roads, possibly using the more ancient
track-ways across Britain, hence covering a larger area with a
greater water supply. However, as has already been mentioned, this
would have slowed the rebels in their advance and given the Romans an
advantage. Additionally, covering a larger upland area in search of
water results in a break-up of the horde as it is fragmented by
individual units following different rivers. Coalescing these units
on command, for example to give battle, would have been slow and
these difficulties would have been the horde's lack of preparedness.
The Roman army practised marching in all conditions and made
provision for carrying water. This cannot be said of the rebel
tribesmen: they would have had water skins and the like, but probably
not enough capacity to cover large distances between replenishment
more, as the horde followed the Romans upstream there may have been
even less water flowing, more pollution and probably a destruction of
the river banks and other physical characteristics. Of course, these
observations are most applicable to roads that parallel rivers, for
example, the Kennet, Wye, Avon (from Bath) and Great Stour
(Canterbury to Ashford).
an aside, the Romans would extract water from a river in a
controlled, disciplined manner so that, for example, animals did not
pollute potable water. The tribesmen probably knew of such practices,
but it is hard to imagine a huge volume of humans and animals
descending on a river after a hard day of marching, maintaining
extraction discipline and not destroying the water source they all
Camp grounds and marching camps
adjacent to rivers
So far we have examined the locations where rivers,
with sufficient flow for either rebels or Romans, intersected Roman
roads; however, both protagonists could have made use of camp grounds
(rebels) and marching camps (Romans) that were adjacent to rivers. In
the case of the rebels this would have allowed them to seek
additional water, other than that along roads, and to have broadened
their marching front, possibly allowing a degree of flanking of the
withdrawing Romans. For the latter the additional use of river
locations would have conferred a level of tactical surprise and much
more importantly, allowed Suetonius to choose a battle site situated
off the road network. However, it should be re-emphasised that
Suteonius would probably have used the road system for most of his
march from London, only leaving the network once he had arrived at
the battle site location: to do otherwise would have diminished his
advantage regarding the differential in marching rates, i.e.
estimated at 13km/day.
To examine the Roman possibilities we can again turn
to the study of known marching camps in Britain and use a
range of statistical and GIS techniques to predict the locations of unknown camps sites elsewhere in Britain. This essay will
extract some of the findings and predicted sites from a detailed
description of the method in an essay available at:
The same essay contains detailed information
relating to the finding of the rebel camp grounds. Additionally,
although this essay displays maps of these techniques along the
Portway, similar UK-wide maps in Tiff format can be found at the URL
In summary, the predictive technique involved the
extraction of key topographical and hydrological attributes for 374 known marching camps across Britain. These attributes were
statistically examined and a range of values discovered that are
thought to represent a description of a suitable camp ground, that
is, the description might match the thought processes of a Roman
surveyor tasked with selecting marching camp locations. The range of
values place a limit, from good to bad, on the various attributes,
for example, the examination of ground water saturation gives an
indication of the level of bogginess that a camp surveyor might have
thought acceptable. The statistical description of the known marching camps was then searched for across the rest of Britain
resulting in the location of areas thought to be the location of unknown camp locations.
Figure 13 displays the results of these techniques
centred on Silchester. Here the most favourable marching camp areas
alongside rivers capable of supplying the Roman demand are displayed,
and show that Suetonius could have marched his army of 15,000 humans
up most river valleys in the region. He also had the capability of
marching across-country from one river valley to another. There are
some river stretches that are not so favourable to the Romans, i.e.
those areas adjacent to rivers in Figure 13 which are not coloured
red; these have attribute values that, in combination, lack the full
level of acceptance that a Roman army surveyor might have demanded of
13: Most suitable Roman Marching camp locations along rivers and
roads. Suitable camps at river-road intersections = black, most
suitable camps along rivers = red. Elements
of this image are © Crown Copyright. All rights reserved 2013.
As an example, much of the lower stretches of the
Kennet Valley, between Silchester and Mildenhall, are not suitable
for the Romans: partly because the ground is too boggy and
water-logged to make a good camping ground.
The red areas in Figure 13 also indicate where
Suetonius could have camped his army in preparation for the final
battle. As already mentioned, Suetonius would probably have kept to
the road system for most of his march from London, but he might have
left it on arriving at the river valley along which he knew he would
find his preferred battle site.
Figure 14 displays the case for the river-side camps
grounds thought suitable for the Boudican horde as it followed
Suetonius. In comparison to Figure 13, the Roman case, the horde's
camping options are more limited: there are far fewer suitable camps
grounds adjacent to roads (black areas) and the number of suitable
river valleys is much lower, coupled with a lack of deep penetration
up the river valleys. Of course, the latter is largely the
consequence of the lack of sufficient water. This observation also
suggests that, for rivers flowing away from the Roman front line
towards the horde, Suetonius could have selected a battle site in the
upper reaches of a river, and have himself found sufficient water:
for the rebels there would have been insufficient.
14: Boudican horde camp grounds alongside rivers and roads. Most
suitable river-side camps = dark brown, less suitable = light brown.
Suitable camp grounds at river-road intersections = black. Elements
of this image are © Crown Copyright. All rights reserved 2013.
The Boudican rebels need
to follow the Romans, matched to their negative disparity in
discipline, experience, march-rate and preparedness, coupled with the
stress imposed by a lack of food, fodder and water, and all further
compounded by the diminution of morale as the horde marched further
from its homeland, can be estimated as strain rates (Figure 15). In
this image, the suitable camp grounds in Figure 14 are weighted by
the factors just described such that, the blue areas show where the
horde is least strained, typically in lower river reaches, while the
red areas indicate maximum strain. The latter are most often found in
the upper reaches of smaller rivers where the effects of a lack of
water, food, fodder, etc. compound to produce the greatest strain.
Here the rebel horde would have been most disadvantaged relative to
Suetonius' army: at its weakest in locations most favourable to
Suetonius' choice of battle site.
15: Boudican horde camping grounds alongside rivers, colour graded
for strain. Highly strained = red-brown, moderately strained =
green-cyan and least strain = blue. Strain levels are computed from
elevation, amount of food and fodder, shortness of adequate water and
distance from London. The values for the strain due to the lack of
food and fodder is proxied by a calculation based on elevation and
local hydrogeological parameters. Elements
of this image are © Crown Copyright. All rights reserved 2013.
Terrain analysis and water
The availability at the battle site of an adequate
water supply would have been more crucial to the Romans than when on
the march. When marching a temporarily inadequate water supply would
have been an inconvenience, as long as it was not prolonged. When
waiting for battle such a situation would have been disastrous. And,
given the disparate marching rates of the Romans and rebels, the
waiting time may have been 4-5 days at, for example,
Mildenhall-Cunetio (116km from London). Therefore, it is considered
inconceivable that Suetonius did not choose a battle site with an
adequate water supply that could be safeguarded and, most probably,
flowed away from his front-line towards the rebel line.
The earlier terrain analysis work
( boudica-terrain-analysis.pdf ) created a list of 263
possible battle sites across the study area (Figure 16), with those
most likely to be the actual battle site located within, or near, the
Kennet river valley. For the present work the 263 were examined and
all those not having sufficient water to maintain the Roman army were
eliminated. A few former sites were moved slightly to more
appropriate positions, and some new sites added. The overall result
is a new list of 110 possible battle sites, a significant reduction
based largely on the hydrology study.
New (110 and red) and old (263 and black) possible battle site
locations overlying terrain. The new sites may overlie the old. The
black dots are old, deselected sites, i.e. those no longer suitable
because they lack adequate water for the Roman army.
sites have been removed in the East Midlands area, while elsewhere
there has been a general thinning of possible battle sites. Of
special note is the removal of many sites along the eastern, lower
stretches of the river Kennet, the preferred location for the battle
in the terrain analysis work, due to the effects of small water
catchments and the bourne-like nature of the local streams, i.e.
there is not enough water.
Figure 17 only shows the locations of the 110 new sites. As with the
old study, few sites are located west of the Fosse Way (Figure 1)
because there is no evidence of the destruction of towns or forts on
or beyond that road, for example at Cirencester, and also because it
is thought likely that if Suetonius had reached the Fosse Way he
would probably have marched immediately to a legionary fort at
Gloucester or Exeter.
As an aside,
the old study's battle site at Dadlington, now thought to be the site
of the Battle of Bosworth, is still in the new list – a good
battle site, meeting the terrain and water needs of a waiting army,
seems to have permanent qualities.
hydrology work clearly demonstrates the critical importance of water
supply to large bodies of marching men and beasts, not only during
the Boudican revolt, but also other Roman era campaigns, for example,
the invasion in 43AD, and the Agricolan and Severan in Scotland. Of
course, the same truth applies to later periods.
17: The locations of 110 possible battle sites based on the former
terrain analysis and the new hydrology work. Elements
of this image are © Crown Copyright. All rights reserved 2013.
and ranking of battle sites
mentioned, the earlier terrain analysis work did not empirically
differentiate between the possible battle sites: any one was as
likely to be the actual site as another. However, for this study a weighting of various
factors, followed by a ranking exercise, was performed on the 110
possible battle sites in order to remove some subjectivity, but not
all, in the selection of a site thought more likely to be the actual site. The key term is 'more likely' because - although the author has
endeavoured to remain objective in the interpretation of Tacitus'
script, terrain features, the hydrology, marching camp calculations
and weighting factors - some other worker would indisputably create a
different ranking order.
weighting factor was derived using GIS techniques in SAGA and then
weighted for each site according to the following formula for
Xi = Each
data point i
XMin = The
minima among all the data points
XMax = The
maxima among all the data points
0 to 1 =
The data point i normalized between 0 and 1
normalised weighting numbers were then summed, divided by the number
of factors, and finally ranked 1 to 110, with 1 being the more likely
to be the actual battle site of this listing.
aim of the exercise is to use the determining factors so that the
battle site is ranked so that the Romans gain the greatest empirical
advantage from the battle site, and the Boudican rebels the reverse.
This strategy is thought most appropriate given that Suetonius chose
the actual battle site, and therefore probably had sufficient time,
understanding and knowledge not to locate the battle to his
disadvantage. Hence, the normalised range was organised such that
zero was the most advantageous to the Romans and, of course, vice
were used for weighting and ranking: each will be described below.
of the battle site from a Roman road
road system conveyed many benefits to the marching Roman army –
speed of traverse, adequate water, good camping ground and
communication with the rest of Britain being most important.
Selecting a battle site that traverses a road would maximally
maintain these benefits, if only in potential. A morale dimension
might also be invoked, namely, the legionaries might have thought
they had an escape route if the battle was lost. Therefore, the
distance of each possible battle site from a Roman road was
calculated within SAGA, and the resulting kilometre values normalised
as described above.
As an aside,
there is another advantage to be gained by following the road system:
the use of previously constructed marching camps. Archaeologists have
shown that known camps in Britain were re-occupied by other units at later dates. This
often resulted in an alteration of the camp margins, or a smaller
sized camp built within and utilising some of the pre-existing
ramparts and ditches. The Boudican uprising takes place only 17 years
after the start of the campaigns to conquer southern Britain. It
therefore seems reasonable to assume that marching camps built during
the conquest, and probably within the 17 years thereafter, would
still be extant. Most would be located along the road system. For
Suetonius' men, as they retreated in front of the Boudican horde,
re-occupying these old camps would have saved them considerable
energy and time. Marching towards an existing refuge might have had a
substantial, positive impact on legionary morale; however, this has
not been modelled.
the Boudican horde was from an adequate water supply
horde required a minimum of 0.04 cumec of water if its camp ground
was located downstream from the Roman front line. Although it could
augment its need from local, smaller streams within the vicinity of
the battle site, nevertheless it would have still needed a river of
that capacity to fully maintain itself. Therefore, the distance of
the battle site to such rivers was measured and normalised. However
there is a twist to this factor.
Boudican horde took its water supply from a source that had already
passed through Roman lines, then the Romans would probably have
interfered with the supply and maybe polluted it with their effluent.
This possibility would further strain the rebels but, because there
is no evidence of such an event or a simple method of assessing the
results, this consequence has not been calculated, or allowed for,
but should be borne in mind when examining each battle site.
As a further
aside, if the Boudican horde was, while on the march and moving
constantly onto fresh ground, already strained by water shortage,
then that debilitation would be magnified by halting prior
to battle, thereby draining the immediately available water. This may
have been part of Suetonius' logistical planning, i.e. significantly
weaken the horde by the route taken, before destroying
it in battle.
strain rates: a multi-attribute factor
multi-attribute factor was calculated to measure the supposed strain
experienced by the rebels as they marched along river valleys or used
roads across southern Britain. The attributes were: distance from
London, elevation, the availability of sufficient water and foraging.
For each battle site these were summed and normalised; Figure 15 is
based on this multi-attribute approach, but only for rivers. The
calculation of the first three strain attributes - distance,
elevation and water – do not require further explanation: not
so, that for foraging.
As we have
discussed, as the rebels marched after the Romans they may have moved
into land where food and fodder resources were limited and water in
short-supply. This would be particularly true for the upland chalk
and limestone regions. In lowland regions this stress would be
lessened by larger local populations producing surplus food in richer
farmland. As a strain indicator related to foraging, the distance
travelled since leaving London might be thought to be significant
but, because the horde probably had little carrying capacity, or
practice, what food was entrained would have run out after perhaps
three to four days. After that time, and for the remaining length of
the campaign, the general provisioning method would have been by
foraging, requisition and pillage. Under these circumstances the
distance travelled is not relevant, i.e. the horde would have
experienced a constant, background strain due to foraging etc. after
3-4 days no matter how far it had already travelled. However, there
would have been an element of declining morale due to the distance
travelled from London, and it is for this reason that this was
calculated separately as a strain indicator.
assigning a constant, background, foraging strain to the lowlands
allows the differentiation of increased strain due to travelling in
upland areas where food and fodder are more scarce. Therefore, the
stress on the horde due to foraging can be represented by a measure
of elevation and hydrogeological parameters: these in combination act
as a proxy for the foraging stress. Consequently, the weighting
method employed was to simply multiply elevation by a hydrogeological
parameter called the Mean Annual 7 Day Minimum (MAM(7)), maps of
which have been produced covering the UK. MAM(7) is essentially a
statistical measure of low-flows in rivers and can be assigned,
crucially for this exercise, to varying lithological and soil
classes. Lowland areas were ignored in this process by identifying
their predominant rock types, e.g. sandstones, shales, mudstones,
while upland areas were identified by their rock type –
typically either chalk or limestone. The result was a measure of
foraging strain but only for the upland chalk and limestone regions.
us that Suetonius chose a battle site located in a defile, with a
plain in front and woodland behind. The previous terrain analysis
study used these basic descriptors to assist in the finding of the
263 battle sites across southern Britain.
descriptors were constrained by criteria (Table 3) but these can
still result in a range of morphological surfaces – for example
of defile shape, height, depth, width, bounding slopes and gradients
etc. – which vary considerably in form, from subdued to robust.
Accepting that the most robust form is the most defensible, then
those of the 110 might have been more favoured by Suetonius.
a defile of approximately 1km width
set within an elevated area
an adjacent, lower elevation plain
(less than 4 degrees of slope) or an extensive, lower elevation
flat area with gentle slopes
a plain of at least 1km diameter to
accommodate the British horde and wagons
a defile whose flanks rise at least
30 metres higher than the bottom of the defile and have a steep
slope (generally > 8 degrees)
the flanks extend at least 1.5km in
both directions to discourage mass flanking movements by the
Britons. These flanks could be a mix of high and broken ground.
A gentle, positive slope (< 5
degrees) exists between the Britons and Romans.
a river or stream, sufficient to
water 10,000 men and 1,000 horses and capable of protection by
the Roman force (note: this water requirement was not calculated)
the Roman army must be able to
march radially away from London using roads to reach the site
a general requirement that the site
cannot be easily flanked, for example by an adjacent road or
battle site should not so intimidate the Britons that they would
not offer battle but instead besiege the Romans – it must
be inviting to the Britons and appear to be a trap for the Romans
3 The selection criteria used in the earlier, terrain analysis study
this desirable defensiveness, the Terrain Ruggedness Index (TRI) was
utilised. This uses elevation changes within neighbouring grid
nodes/cells to determine the heterogeneity of a terrain. Typically
this heterogeneity is characterised by type, e.g. level terrain,
slightly rugged and highly rugged. SAGA was used to characterise the
ruggedness of terrain within a 1km radius of possible battle sites.
The resulting values were then normalised, 0 to 1, with 0 being the
most rugged and, therefore, the most advantageous to the legionaries,
and the most likely to have been chosen by Suetonius.
due to limiting factors associated with battle sites
The body of
110 possible battle locations contain some that have limiting
features, unfavourable to the Romans, that cannot be readily measured
by calculation and must be visually evaluated.
battle sites which the Romans could only have reached by performing
a marching u-turn. The
assumption is that the Romans marched radially away from London, but
to reach retrograde battle sites would have had to reverse, to
varying degrees, their line of march. This action would have exposed
their marching and battle-line flanks to attack from the following
rebels. For example, such sites are common along the western-facing
scarp of the Chilterns. In these cases Suetonius might have marched
north out of London along Watling Street, continued beyond the NW
face of the Chiltern escarpment and then turned south-westwards,
parallel to the escarpment, and marched towards his pre-chosen
battle site, the defile, ensconced within the NW facing escarpment.
This convolution of manoeuvre was considered during the phase of the
investigation when objectivity in selecting terrain analysed sites
was paramount, i.e. these sorts of sites (there are quite a few
throughout the southern Britain) match the terrain
description/criteria and should not be dismissed, but instead
down-weighted as likely battle sites.
15: Battle sites within, and adjacent to, the Kennet river valley. Elements
of this image are © Crown Copyright. All rights reserved 2013.
possibility of the Romans being flanked. Depending on the local terrain, marching routes and other factors,
some sites have been weighted negatively due to the possibility of
flanking by the rebels. To be clear, this flanking relates to local
outmanoeuvring at the battle site and to flanking approach-marches
by the rebels that may take place over a number of days. To aid the
discussion we will examine a region of the Kennet river valley
(Figure 15). The Kennet river is that shown running through
Eddington, Axford and Mildenhall-Cunetio. An example of sites that
had little danger from flanking are Eddington, Mildenhall-Cunetio
and Ogbourne St. George because the rebel horde would have had to
approach the Roman battle lines along the line of march. However,
Axford being in the river valley, could have been flanked by rebels
taking the road to Mildenhall-Cunetio. In contrast, at
Mildenhall-Cunetio the same road and river valley converge, both
could be blocked by a defensive line which might have enabled the
Romans to force the rebels to march directly towards them. The sites
at Marten and Brunton could be flanked, both requiring an element of
eastwards, retrograde rotation from the Roman line of march.
However, because Marten could have been more readily reached by
rebel units cross-country marching from the main Roman road than
Brunton, it is weighted down more heavily. All 110 possible sites
were examined in this way and each weighted accordingly from 0, no
flanking possibility, to 1, high chance of flanking.
battle site has a river that flows towards the Roman front lines then it has been down weighted.
due to direction of march from London
London is the
last named location given by Tacitus for Suetonius and his army. The
obvious question is which direction of march did he take? The answer
is the primary supposition of any study of Boudica's last battle
site, and of course, delimits the region in which to search.
16. Which direction from London did the Romans march? Answer: west
to Silchester. The red lines separate the differing directions
Suetonius could have marched.
terrain analysis work examined this question in depth, its results
are itemised in Figure 16. In summary, it is thought that Suetonius
while retreating would have marched his army directly westwards,
crossed the Thames at Staines, thereby probably gaining at least a
day on the horde, before moving quickly along the Portway to friendly
Silchester (Figure 1). At some point west of Silchester, but not
necessarily directly west there being four westerly roads out of the
town, he chose to alter
his strategy of retreat, or withdrawal, and offer battle. This last
point we are told implicitly by Tacitus when he writes, "when
he [Suetonius] prepared to break off delay" and fight a battle.
assigned to regions (Figure 16) is 0 for a westwards march from
London, 0.25 for marching south, 0.75 for marching north, and 1 for
an eastwards march. This weighting is a reflection of the author's
combined suppositions (text in Figure 16), with the lowest value
thought most likely, i.e. westwards. The southern route is also quite
likely, and so is given a weighting of 0.25. The northern route is
considered very unlikely, reflected in a weight of 0.75. The
eastward, suicidal route, is thought to be highly improbable and
given a weight of 1. However, of the 110 sites, none are in the east.
ranking process and list of likely battle sites
normalised weightings described above were summed for each possible
battle site, divided by six and then ranked 1 to 110, with 1 being
the more likely - of this study's selection of criteria, weightings
and suppositions - to be the actual battle site (see Table 4 and Figure 17).
4: The 110 possible battle sites ranked in order, with 1 the more
weightings for each site ranged from 0 to 1 except for ruggedness,
the measure of terrain fitness best suited to the Romans, which was
increased by 50% to match its probable importance in Suetonius'
Top 40 rankings after removal of weighting due to direction of march
17: Ranked battle sites overlying terrain and Roman roads. Top ten sites
are in red, 11 to 20 in magenta. Cross-reference the ranking numbers
with Table 4 to identify the locations. Elements
of this image are © Crown Copyright. All rights reserved 2013.
discussed, the primary supposition of any study such as this, is the
direction Suetonius took when leaving London. If this weighting is
removed from the ranking process then a new listing (Table 5, top 40
sites only, and Figure 18) of possible battle sites is created.
in Buckinghamshire is sited in the northern march region (Figure 16)
but, once this weighting is removed (Table 5 and Figure 18), it
displaces Ogbourne St. George as number 1 which is relegated to
number 3. Overall, the removal of the weighting for direction of
march still leaves a predominance of western sites at the top of the
18: The battle site rankings where the weighting due to the marching
direction from London has been removed. Background as
Figure 17. Top ten sites are in red, 11 to 20 in magenta.
Cross-reference the top 40 ranked numbers with Table 5 to identify
the locations. Elements of this image are © Crown Copyright. All rights reserved 2013.
We have now
examined the combined results of the earlier terrain analysis, the
water needs of the legionary and rebel forces matched to the
available water supply, and an examination of the marching camp data
that places limits on where Suetonius might have marched and camped
and, hence, the location where the final battle might have taken
ranking battle sites (Figure 17) occur in an area from the Kennet
valley region through to the Chilterns, and also in the high
Cotswolds, within and near the Evenlode and Windrush river valleys
(Figure 19). Elsewhere groupings are found within the South Downs of
West Sussex (East Meon, Milland and Bowyer's Common) and in the south
facing valleys of the hills north of Dorchester (Piddlehinton,
Stratton and Winterbourne Kingston). The former are thought less
likely to be highly probable sites because of their distance from
London; however, if Suetonius had marched in this direction, with the
intention of reaching the ports at Portchester and Chichester, then
their likelihood increases; this probability is tinged with doubt
when considering Suetonius' probable nature, i.e. would this man
consider a strategy which might lead to flight to the continent? The
latter are fine examples, but again, probably too far from London to
be seriously considered as likely sites; however, they should not be
discounted entirely, especially if it is thought Suetonius had been
manoeuvring in the direction of support from the 2nd Legion probably located in Exeter.
Cotswolds locations (Wiggington, Lower Slaughter and Upper Swell)
pose a difficulty with the favoured westwards march out of London
because they imply a London - St Albans – Bicester
– Cirencester marching route as being more probable. Indeed,
passing through St. Albans would match Tacitus' account, and
archaeological evidence, of destruction. It is equally possible, and
preferred by the author, that St. Albans was devastated by the rebel
unit that had earlier destroyed the 9th Legion and then followed Suetonius as he marched to London.
19: High ranking battles sites in the high Cotswolds. Numbers are
of this image are © Crown Copyright. All rights reserved 2013.
Suetonius may have taken was London – Silchester – Goring
Gap – Bicester – Cotswolds, with the initial intention of
moving on to Cirencester, before terminating at Gloucester, the
legionary fort for the area.
ranking sites in the high Cotswolds, West Sussex and Dorset result
from the same measurements, weightings and calculations as those in
the Kennet valley region and should not be dismissed, even if that
implies a route taken that is contrary to this author's preferred
westwards marching route.
20: High ranking battles sites around Mildenhall-Cunetio. Numbers are
of this image are © Crown Copyright. All rights reserved 2013.
Within a 17km
radius of Mildenhall, in the Kennet valley region (Figure 20), are
eight possible battle sites, including Ogbourne St. George at number
one. This might be considered a remarkable outcome of the work
described in this essay, but might have already been fully
appreciated by Suetonius. But not only Suetonius: the East Kennet
battle site was also the precise location of a battle in 1006 between
Vikings and Anglo-Saxons, while the Kennet Valley at Newbury saw two
battles of the English Civil War in 1643 and 1644.
Governor of Britain, probably selected for his military prowess and
experience, turned impending disaster into victory, securing the
Roman province for the next 350 years. It is instructive to compare
this outcome to Varus' defeat in the Teutoberg in 9AD: Germany does
not become a province, nor its inhabitants Romanized, while southern
Britain is pacified and Romanized. It might be argued that Suetonius'
achievements have been underestimated.
handling of the Boudican campaign might not be fully appreciated.
Admittedly, his probable original plan, of containment of the
uprising in eastern England, went badly wrong when the 9th Legion was routed and the 2nd refused to obey his orders; the first disaster might have been the
Governor's responsibility, but the second could not have been
foreseen. However, after leaving London it seems Suetonius made all
the right decisions.
He may have
called upon his experiences of fighting tribal units in the arid
regions of Mauritania and the Atlas Mountains to realise that the
size of the Boudican horde, coupled with its inexperience of
distance-marching in regions with a scarcity of food, fodder and
water, might eventually result in victory.
would have realised that the rebel leaders had to destroy him in
battle before he found refuge in a legionary fort, or support from
the 2nd Legion. They therefore had to follow him, even if they were placed in
logistic jeopardy. Suetonius might have reasoned that marching his
superior and well-trained, -practised, -provisioned, -equipped and
faster legionaries into high and dry land would strain his
adversaries far more than his units. He might have planned that
eventually the Boudican horde would be so weakened that it could be
destroyed in battle. But, if not weakened sufficiently, his quicker
army would still be able to escape to a legionary fort in the west
country, and then plan the re-conquest.
it is postulated most likely that Suetonius led his soldiers out of
London along the Portway (Figure 1), crossed the Thames at Staines,
and marched on to his kingly ally, Cogidubnus, at Silchester. From
Silchester he marched directly westwards, taking the Ermin Street
spur towards Mildenhall and Bath, and into the high and dry chalk
uplands of the White Horse Hills (Figure 3) and an already identified
battle site. His decision to offer battle would have been influenced
by many factors, but surely amongst the foremost might have been the
planned, debilitating and destructive effect on the Boudican horde
of marching over 116km from London to Mildenhall-Cunetio, that is
seven to eight days at 16km/day (probably longer as the logistical
marching rate of the legions confers another advantage on the Romans,
namely, being approximately four to five days at the battle site
before the slower Boudican rebels arrive. Time enough to rest,
recuperate, repair equipment, gather or consume the fodder in front
of the lines and prepare the ground, water-supply and defences for
either a siege, or battle. Long enough to again emphasize the
critical importance of having sufficient water. Unfortunately for the
rebels, if they came off the march in a battle location without
sufficient water, fodder or food, then their already strained state
would be compounded.
to one striking oddity of the battle: why did the Boudican rebels
frontally attack and not besiege and weaken, or extensively flank,
the Romans? To answer that definitively is not yet possible, however,
if Suetonius chose a battle site where he controlled the water
supply, had already consumed or gathered the local foodstuffs, or the
rebels had insufficient nearby water, then they may have been forced
to quickly attack in their march-weakened state, or disperse. It is
possible to envisage Suetonius, a man probably well-versed in Julius
Caesar - “conquer[ing] the foe by hunger [and
thirst] rather than by steel” - deliberately choosing such a site, knowing that his legionaries
would use their steel to finish the foe already weakened by his
In support of
the preceding paragraphs are insights into the experience and
character of the Roman commander, so critical to the outcome of the
uprising, given by Tacitus in his Histories when describing the
battle of Cremona during the Civil War of 69AD, “for
he was naturally inclined to delay, and a man who preferred cautious
and well-reasoned plans to chance success. So he kept issuing orders
to fill up the ditches, clear the fields, and extend the line,
thinking that it was soon enough to begin to conquer when they had
made provision against defeat.“
cannot be reasonably denied that the study of terrain analysis,
hydrology, marching camps and logistics is beneficial when cautiously
applied to the enigma that is the Boudican uprising: to what extent
is debatable - for now.
comments go to the heart of what the author is attempting, that is,
to narrow down the search for the battle site by combining
archaeology and historical accounts with modern data and computing
techniques. However, not one site, or any listing, is sacrosanct as
the data, methodology and results are improved.
undoubtedly true is that the merciless objectivity of the
archaeologist’s trowel will, hopefully, end the search.
Grant, Michael, (1973),
Tacitus: The Annals of Imperial Rome,
Kenneth, Wellesley, (1995), The Histories,
Primary references for
Jonathon, (1999), The
Logistics of the Roman Army at War (264 B.C. - A.D.235), Columbia
Studies in the Classical Tradition.
John, (2005), Conquest:
The Roman Invasion of Britain,
Veterinary Department, Great Britain, (1908), Animal
Printed for H.M.S.O by Harrison and Sons.
Development Directorate United
States army, (2008), Water
Primary references for
T. J. and Hannaford, J. (Eds), (2011), UK
Hydrometric Register. Hydrological data UK series. Centre for Ecology & Hydrology.
Bullock, A. and Dixon, J, (1992), Report
No. 108. Low
flow estimation in the United Kingdom,
Institute of Hydrology (NERC).
Marshall, D., and Sutcliffe, M., (1987), Report
No. 101. Low
flow estimation in Scotland, Institute
of Hydrology (NERC).
(2001), Low Flow Hydrology: a review, Journal of Hydrology,
SAGA, System for
Automated Geoscientific Analyses, http://www.saga-gis.org/en/index.html
essay is Copyright © Steve Kaye and protected under UK and
international law. May be used free of
charge. Selling without prior written consent prohibited. Obtain
permission before redistributing. In all cases this notice must
within this essay, specifically the original marching camp data and
Roman roads, are © Crown Copyright. All rights reserved 2013.
This copyright is acknowledged for all images and text in which such
1: Limitations and caveats
work described in this essay will be improved as new data and
techniques are investigated, meanwhile, the following points outline
the limitations and caveats the author considers most important.>
majority of the findings are derived from SRTM data at a grid
spacing of 90 metres. This
spacing limits the resolving power of many of the techniques. The
author is hopeful of acquiring a sound topographical dataset at a
higher resolution: 50 or more preferably, 25 metres.
hydrology calculations are based on the SRTM 90 metre data and
consequently suffer from the limitation of resolution discussed in
point 1). The author hopes to acquire a sound hydrological grid in
method used to calculate the river flow statistics is based
primarily on rainfall, evapotranspiration and surface flows. It does
not involve calculations of ground water processes, for example,
aquifer discharge to rivers. Additionally, the naturalised flow
calculations are at the very extreme of what is thought possible
given the minimal flows involved; consequently, some postulated
battle sites, located alongside rivers supplying the minimum of
demand, may not be viable. Nevertheless, the present results are
surprisingly well-correlated with the limited published data from
the Centre for Ecology & Hydrology (CEH).
to the SRTM limitations already mentioned, the width and breadth
measurements of the Roman marching camps were not used to extract
the various indices used in the study. Instead
a simple, circular buffer was placed at the known centre of the
camp, the radius of which was based on the longest known side of the
camps. This is thought to be acceptable at a 90 metre resolution,
but not so if the base grid is improved in the future to 50 or 25
SRTM 90 metre grid described above limits the resolution of all
resultant calculations and, necessarily, creates some location
'jitter' in the placement and calculation of factors related to
rivers, roads and various attributes. This 'jitter' has its most
obvious effect at the 10s of metre scale but does also effect larger
measures of scale, size and attributes resulting from calculations
based on these scales.
Roman road dataset has not been parsed to separate those built and
used by the military from those of civilian construction and use. It
could be argued that most, if not all, roads in Scotland and Wales
are military, but that is not the case for England. These issues
will be tackled in future work.
of the prediction of marching camp locations is based on the
selection of various statistical methods thought most applicable to
the issue at hand. Therefore, there exists a subjectivity in the
methods selected. This is unavoidable in most cases, and will
theoretically always be the case, nevertheless it is hoped to
improve the statistical methodology after the resolution and
hydrological issues have been solved (points 1 and 2).