Boudica: Terrain Analysis

Contents:

• Start
• The terrain analysis method
• Opening events leading to the battle
• Which way out of London?
• The Kennet river valley
• The battle

 

Summary of events in 60/61AD

A précis of events in 60/61AD based on Tacitus would mention that Caius Suetonius Paullinus 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 have reached Suetonius as he marched from Anglesey towards London with cohorts and auxiliaries from the 14th and the veterans of the 20th Legions, numbering, according to Tacitus, 10,000 armed men. Hearing that the 2nd Legion, based in Exeter, was not, as Suetonius had ordered, marching to join him would more than double the bad news. 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 numbered in the hundreds of thousandsii. On reaching London he decided to abandon the proto-city, marched his men, and 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 he was forced by circumstances to offer battle. The Roman legionaries, auxiliaries and cavalrymen were victorious, apparently killing tens of thousands of Britons for little loss.

Finding the site of Boudica’s last battle: an approach via terrain analysis.

For many years archaeologists, historians and other interested parties have sought the location of Boudica’s last battle in AD60 or 61 using the sparse archaeological evidence, the accounts of Cornelius Tacitus and Cassius Dio and, to a greater or lesser extent, various insights or specialised knowledge, frequently military. This essay is a description of an attempt to find likely battle sites using terrain analysis techniques.

Figure 1: Location names, tribes, Roman roads and legionary bases.

The Method

The aim of this study was to marry the primary written account, that of the Annals written by Tacitus in 109AD, with satellite-derived elevation data and to use the result within a computer program designed for geographical and terrain analysis to find likely battle sites across the southern UK. The elevation data are the Shuttle Radar Topography Mission (SRTM)³ at 90 metre resolution which, when manipulated within SAGA⁴, the computer program, allows the display of terrain features such as rivers, slope, ridges, the concavity or convexity of slopes, aspect and, particularly important for this study, river valley bottoms and plains. Other information loaded to SAGA, and used to aid the investigation, included Roman towns, forts and roads (Fig.1). Having built a terrain model the next step was to match Tacitus’ account with the terrain features.

Tacitus was a Roman senator, consul and the son-in-law of Gnaeus Iulius Agricola who, at the time of the Boudican revolt, was a tribune with one of the legions stationed in Britain. As a senior officer of senatorial rank, Agricola would have been very involved in the details of the Roman campaigns in Britain; he may even have been present at Boudica’s last battle, but he certainly would have narrated an accurate and detailed account of the battle to Tacitus. Unfortunately, the Annals is a year-by-year account of the history of imperial Rome and necessarily has to briefly cover a large number of events. The same is true for the description of the battle site, the key passage being:

14.30.34. Suetonius had the fourteenth legion with the veterans of the twentieth, and auxiliaries from the neighbourhood, to the number of about ten thousand armed men, when he prepared to break off delay and fight a battle. He chose a position approached by a narrow defile [faux], closed in at the rear by a forest, having first ascertained that there was not a soldier of the enemy except in his front, where an open plain [aperta planities] extended without any danger from ambuscades. His legions were in close array; round them, the light-armed troops, and the cavalry in dense array on the wings. On the other side, the army of the Britons, with its masses of infantry and cavalry, was confidently exulting, a vaster host than ever had assembled, and so fierce in spirit that they actually brought with them, to witness the victory, their wives riding in waggons, which they had placed on the extreme border of the plain.

Clearly the meaning of the Latin word faux is critical. In various Latin dictionaries it is translated as throat, gullet, jaws, gorge, ravine, chasm, isthmus, pass and defile. Typically in modern translations of Tacitus it is defined as meaning a defile, a terrain feature that is robust, not gracile: a feature with significant elevation changes. Faux does not seem to apply to shallow-banked river valleys or indentations or hollows in gently rolling terrain.

Tacitus later states the Roman army “kept its position, clinging to the narrow defile as a defence”⁵. The key topographical elements are the defile and plain which in turn suggest the location is similar to, but not exclusively, that found at escarpments where low, relatively flat ground abuts ground that rises sharply and is commonly wooded even today. Within the face of escarpments are frequently found narrow defiles cut by rivers, streams and periglacial action. Tacitus even limits the extent of the plain by stating that the Briton’s wagons are placed on the “extreme border”. The width of the defile can be estimated from the “close array” of the legions (approx. 0.5 to 1.0 metre per legionary) and the standard Roman practice of having ranks of cohorts behind the frontline that act as reserves. Without knowing the precise numbers of legionaries, or others making up the “ten thousand armed men”, an estimated defile width of 750 to 1250 metres seems reasonable.

Although Tacitus’ description allows for little misunderstanding in its gross form, i.e. a defile facing an open plain, an extremely complex algorithm would be required to search a digital terrain model for such features, and allow sufficient flexibility such that subtle variations would also capture battle sites that do not match the gross description. For this reason the list of possible battle sites for southern Britain in Table 1 has been derived from visual examination of the terrain model using the following criteria:

1. a defile of approximately 1km width set within an elevated area

2. an adjacent, lower elevation, plain (less than 4 degrees of slope) or an extensive, lower elevation, flat area with gentle slopes

3. a plain of at least 1km diameter to accommodate the British horde and wagons

4. a defile whose flanks rise at least 30 metres higher than the bottom of the defile and have a steep slope (generally > 8 degrees)

5. 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.

6. A gentle, positive slope (< 5 degrees) exists between the Britons and Romans. Roman commanders naturally prefer to charge down-slope, although, there are instances of the reverse

7. a river or stream, sufficient to water 10,000 men and 1,000 horses and capable of protection by the Roman force

8. a general requirement that the site cannot be easily flanked, for example by an adjacent road or valley

9. the Roman army must be able to march radially away from London using roads to reach the site vicinity

10. the 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

Figure 2 shows two examples of possible battle sites at Wendover and Chivery within the western escarpment of the Chilterns. There is a close correspondence of the topography, and general situation, to the criteria listed above and to Tacitus’ description.

Figure 2: Example of two battles sites (Wendover and Chivery) along the Chiltern escarpment. The pink-red colour, in low lands and valley bottoms, marks the location of plains (slopes less than 4 degrees). Bounding graticule in metres, British Grid; rivers are computer generated.

The criteria were not held rigid when selecting sites: often one criterion was given precedence over another. In passing it should be noted that relatively few sites are located across Roman roads, this being quite natural, as road construction would avoid steep ground if possible. In other instances, for example along the west-facing Chiltern escarpment (Fig.3), the Romans would need to lead the Britons to the preferred battle site and this necessitated leaving the easterly to westerly traversing road and march across country before arriving at the westerly-facing battle site. Some battle sites are reached after at least half a day’s march across country, while some are 15km or more from a road and would have taken a full day to reach (normal marching rate on roads = c. 20 Roman miles/day or 29 kilometres).

The battle sites marked on Figures 3, 4, 5 and 6 have been placed in the most optimised positions with regard to the criteria listed above and after examination of various maps but, in reality, each could be re-sited by 10s or 100s of metres depending on conditions in the general vicinity – conditions that might be only apparent when the site is visited.

In the south of Britain there are few possible battle sites selected west of the Fosse Way (Fig.1) because there is no archaeological evidence for the destruction of forts or towns on or west of the road, for example at Cirencester.

Table 1. Click here (opens in a new tab) for a list of 263 possible battle sites (no ordering is implied by the number system).

Figure 3: Battle site locations (black dots) and numbers (for cross-referencing with Table 1) for the North West quadrant of the study area. Roman roads and towns (red dots) shown for location purposes. Wroxeter (red star) was a legionary fort.

Figure 4: Battle site locations (black dots) and numbers (for cross-referencing with Table 1) for the North East quadrant of the study area. Roman roads and towns (red dots) shown for location purposes. Longthorpe (red star) was a legionary fort.

Figure 5: Battle site locations (black dots) and numbers (for cross-referencing with Table 1) for the South East quadrant of the study area. Roman roads and towns (red dots) shown for location purposes.

Figure 6: Battle site locations (black dots) and numbers (for cross-referencing with Table 1) for the South West quadrant of the study area. Roman roads and towns (red dots) shown for location purposes. Gloucester and Caerleon (red star) were legionary forts.

Figure 7: Battle sites (black dots) and geographical names for the study area overlying elevation data.

Examination of Figures 3,4,5,6 and 7 shows that the terrain analysis results in possible battle sites predominantly located in the chalk and limestone regions of Britain and particularly at the margins of these upland areas. Of course, the converse is true, with very few sites located in the lowland regions except where relatively deep incisions by rivers have created the required profiles. Of particular note is that there are only one or two sites within the Iceni and Trinovantes tribal areas of eastern England.

The initial visual selection for southern England, which did not take into consideration any strategic or political concerns but is solely based on the criteria previously mentioned, identified 263 possible sites. Examining the words of Tacitus and applying some simple observations may help identify the area in which the actual battle site is located.

Opening events leading to the battle

Tacitus recounts how the Iceni and Trinovantes rose and attacked Colchester, the Roman colonia in Essex populated by retired legionaries. The news of the uprising would have reached Suetonius Paullinus, the Roman Governor, in or near Anglesey a few days later (see Fig.1).

On hearing the news Suetonius assessed that the subjugation of the Druids on Anglesey was almost complete; that his main legionary forces were located with him (the 14^th Legion and the veterans of the 20^th Legion) while the 2^nd Legion was in Exeter and the 9^th Legion was probably in Longthorpe and other local forts. Suetonius was a very experienced, prudent commander, having successfully crushed uprisings in the Atlas Mountains⁶ and Wales, and well versed in assessing the full import of the news that reached him, namely, the warriors of the whole of eastern Britain had risen, that hot-heads and discontents from other tribes were rushing to Boudica’s banner and that he must snuff out the rebellion quickly or face losing the whole province. He would already know that preparations for the Anglesey campaign meant that his supplies for the year had been concentrated in and around north Wales, and that throughout the rest of Britain the supplies available were sufficient for the local garrisons but not for a prolonged campaign by a concentrated force. The exception might have been the Channel forts and ports at Reculver and Richborough (Fig.1) but these were far away, the wrong side of the uprising and large parts of the Roman supporting fleet, the Classis Britannicae, had been supporting his campaign in Anglesey and that the remainder in the Channel region were probably not capable of transporting large quantities of fresh supplies to him. Suetonius might therefore have decided to conduct an enclosing, crushing campaign by all the forces available to him that were capable of independent action with the supplies they already held. Above all else, the revolt had to be crushed quickly and before winter if Suetonius was to avoid a protracted uprising.

Consequently, he and his units of the 14^th and 20^th Legions may have marched down Watling Street towards London but probably halted at or near Towcester to assess the situation before intending to move eastwards into Iceni and Trinovante territory. The 2^nd Legion may have been commanded to leave Exeter and march to London, with the probable intention of requisitioning supplies from the merchants there, before marching in an easterly or north-easterly direction into Trinovante territory and approaching Colchester. Meanwhile, the 9^th Legion under Petillius Cerialis⁷ may have been ordered to form the northern pincer of this encircling movement and to march in a south-easterly direction (taking the axis Godmanchester-Cambridge-Colchester). The 9^th was the garrison legion for the area to the north and west of the Iceni tribal lands and Suetonius might have required it to hold the forts it already occupied to form a barrier to northwards expansion of the revolt and to dissuade any rebel reinforcements arriving from the Coritani in the north (Fig.1). For this reason possibly only the veteran cohorts, some auxiliaries and cavalry of the 9^th Legion marched with Cerialis.

Some commentators suggest that the 9^th Legion marched independently southwards to face the rebels, possibly at the plea of the citizens of Colchester, or that Suetonius ordered the one Roman legion in the vicinity to put down the uprising alone. Firstly, neither Cerialis, nor any other Roman legionary commander expecting future promotion, would advance his legion without having first received orders from his commanding officer to do so. In support, it is worth noting that Cerialis became Governor of Britain in 71AD. Secondly, Suetonius would have been aware of the size of the uprising (the Iceni and Trinovantes may have been the most populous and
richest of Britons, much like the people of Norfolk/East Anglia during the Middle Ages); that the Iceni were extremely warlike and had risen earlier before being crushed in battle in 47AD; that the Britons throughout the island were deeply unhappy about the slaughter of their Druidic priests on Anglesey and that, consequently, this already large uprising would grow and be difficult to suppress. Therefore it is unlikely that he would have ordered a single legion to suppress the revolt and at the same time to maintain its presence in the local forts. In addition, Suetonius’ character and experience suggests a man of deep military pragmatism: he might not have unduly concerned himself with the fate of Colchester but, instead, might have concentrated on marshalling all of his forces to crush the rebel tribes with the sole intention of putting down the revolt and saving the province. At least, that might have been his plan but it quickly went awry.

For at Colchester Tacitus recounts that the “temple where the soldiers had assembled, was stormed after a two days’ siege. The victorious enemy met Petillius Cerialis … who was coming to the rescue, routed his troops, and destroyed all his infantry” ⁸. Cerialis retreated with his remaining cavalry to a fort. The number of infantry killed is not known but Tacitus does say that 2,000 legionary replacements arrived from Germany in the aftermath of the final battle⁹ and that the 9^th Legion had their number made up - suggesting that a significant portion of the 2,000 went to the 9^th. If Suetonius’ plan was to encircle the rebels then he had just lost the northern arm: whatever the plan, this was a very serious event that endangered the whole province.

At about the same time as the 9^th Legion was routed, Suetonius would have heard that Poenius Postumus, the acting commander of the 2^nd Legion in Exeter, was refusing to obey Suetonius’ order to march and help put down the revolt. No reason for the refusal is given¹⁰. It can be reasonably expected that Suetonius might have ordered the actual commander of the 2^nd Legion, and/or other senior officers and a cavalry unit, to march to Exeter, relieve Postumus of his command and bring the 2^nd eastwards as rapidly as possible. We do know that the 2^nd Legion was not present at the final battle with Boudica but it may have been en route and might have played a significant part in Suetonius’ strategic plans prior to the battle.

Suetonius had now lost the northern and southern arms of his encircling force, if that is what he was planning, and was only left with those forces he directly controlled, the 14^th Legion and the veterans of the 20^th Legion, together with an unknown number of auxiliaries¹¹ and cavalry, located somewhere along Watling Street between Chester and London (Fig.1).

Tacitus continues his account by stating that, “Suetonius, however, with wonderful resolution, marched amidst a hostile population to Londinium”¹². This tells us that the local population, and possibly the Boudican rebels were harassing him as he marched south and that he did arrive in London. Unfortunately, Tacitus does not state specifically that the 14^th and 20^th Legions were with Suetonius and this omission has led to some commentators¹³ suggesting that Suetonius swiftly rode to London with a cavalry unit, but without his legions, assessed the situation, declared that London could not be held, offered to escort citizens to safety and then dashed back up Watling Street to his waiting infantry before offering battle somewhere along the road. However, there is no literary evidence that this did happen and it is far more plausible that Suetonius arrived in London with his legions.

For example, Nicholas Fuentes¹⁴, in summarising the reasons against a cavalry dash, included the cautious, prudent and experienced character of Suetonius; the disastrous consequences of Suetonius not re-establishing contact with his infantry; the damaging effect on the morale of the infantry as he rode away to London; that as the Governor for two years he would not need to travel to London to assess its defences and, finally, that few refugees could keep up with the pace of a cavalry unit as it returned rapidly up Watling Street. To these existing reasons, more can be added.

Continuous communication between Roman legionary units, forts, supporting navy, supply depots and the army headquarters was always of great importance to the Romans. For Suetonius to have left his headquarters for the cavalry dash southwards would result in a loss of communication between the army commander and the rest of his units in Britain. To have broken communication, or at best greatly delayed the transmission of news and orders to and from the commander, at a time when the whole of the eastern province was in violent uproar, the only colonia had been destroyed, the 9^th Legion routed and the 2^nd Legion was not obeying orders, would have been unthinkable.

Another reason against the cavalry dash is the poor martial rigour, even insubordination, of Suetonius’ legions when faced with hordes of fanatical Britons. This behaviour was displayed on Anglesey when the opposing armies faced each other. Tacitus says the enemy, “scared our soldiers by the unfamiliar sight, so that, as if their limbs were paralysed, they stood motionless, and exposed to wounds.¹⁵” Suetonius had to appeal to his men, to urge them on, before they launched their attack and destroyed the enemy. These same men, many of them veterans of campaigning in Briton, were with Suetonius as he marched south along Watling Street: men who did not obey the commands of their unit commanders to engage the enemy, men who were so terrified by the Britons that they stood rooted to their positions in the line and only obeyed commands when given by their army commander, the Governor of the province, Suetonius. He, the only capable man, imploring and commanding his infantry, restored the combat effectiveness of the army. It is unlikely that Suetonius would gallop away from these suspect troops and leave them with officers whose orders, in the heat of battle, they did not obey – in these circumstances Suetonius might have thought that he would return to a scene of massacre. Also, no doubt to Suetonius’ private despair, this episode indicates that the legionary officers were not capable of commanding their soldiers when the need was greatest. He could not leave his men!

And surely, rather than Suetonius march to London with a cavalry unit to gather information, it makes more sense for him to have delegated the task to an experienced but younger officer? Plus, in 60/61AD Suetonius was probably a fit, fifty to sixty year old man used to spending his day in the saddle but, nevertheless, he would be aware that a younger man would have had a better chance of speedy success.

Finally, this militarily improbable, and improper, action would have been mentioned by Tacitus: he does not explicitly state that the legions were with Suetonius in London, because that was to be expected.

Therefore, in conclusion, it is more plausible and most likely that Suetonius and his army marched together down Watling Street, harassed by the rebels, slowly losing soldiers to ambushes and hit-and-run tactics and being aware that the horde of Britons that had routed the 9^th Legion might be on their left flank. It is possible that this horde partially burned and destroyed St. Albans (Fig.1) as it followed Suetonius’ legions to London.

Having reached London Suetonius had to urgently assess his strategy, which essentially amounts to deciding on the direction of march for his army – north and back along Watling Street, east and into the rebels heart-land, south and across the Thames or, west and towards his only other significant armed unit, the 2^nd Legion. This decision obviously determines the most likely area for the site of Boudica’s last battle.

However, before examining these strategic directional decisions in some detail, a few notes on the general situation might be appropriate. In probably no more than three weeks, possibly two, the Romans have been reduced from being the rulers of most of southern Britain, the suppressors of the Welsh tribes and the destroyers of the Druidic enclave of Anglesey, to hunted fugitives, either ensconced in their forts in the north and west country or about to be overwhelmed by a frenzied attack on London. The 9^th Legion has been destroyed as an effective field unit and Suetonius can only hope that it can hold the forts it already occupies. We do not know the manner of the 9^th Legion’s rout but a rebel ambush, in overwhelming numbers, while the unit was marching is probable. In the Roman mind this tragedy would invoke memories of the German disaster in 9AD when Varus lost three legions in the Teutoburg Forest. It is reasonable to assume that many Britons would also know of this event, and other more recent Roman defeats in Britain, when Roman forces had been surrounded or, at least, out-flanked by superior numbers of marauding warriors in terrain least suited to the disciplined, collective defence of the Roman legions.

The reversal of relative strength, detrimental to the Romans but beneficial to the rebels, must have been shockingly clear to Suetonius and his senior staff. When the rebels arose the Romans could march four legions, from positions of strength in the west and north, in their attempt to enclose and then concentrate their forces against the Iceni and Trinovantes. Now the only Roman force facing the rebels in the field, Suetonius’ army, has been pushed by rebel forces, and pulled by the need for supplies and a refuge, into an unfortified, indefensible London. Fortunately London was the nexus of the road system in Britain and this allowed Suetonius to determine the right direction to move away from total destruction and towards a strategic position where he could regroup, resupply, reinforce and then relaunch the suppression of the rebels. So, which direction out of London did he take?

Which way out of London?

To move eastwards or north east, into the Iceni or Trinovantes tribal lands, and bring them to battle would have been the most imprudent option for several reasons: Suetonius’ legionaries may have been tired after their long, harassed march from north Wales; they may have been demoralised by the rout of the 9^th Legion and the refusal of the 2^nd Legion to come to their aid; they would be out-numbered in the home land of their enemies; they would know that they could be readily out-flanked by the mobile Britons, that the possibility of encirclement and destruction was high; that there are very few locations where the terrain would aid them and that they would be marching away from any assistance. To many legionaries the prospect might appear as a death-march, with fearful reminders of Varus’ fate. For Suetonius all of these points, together with his doubts about the fortitude of his legions, would be clear, as would the knowledge that his 10,000 men might be out-numbered by ten or twenty fold and that communication with the rest of Britain would be cut. He may have wondered how he would escape an ambush by such a force or how his men would survive if the Britons chose to encircle and starve them into submission, rather than engage in battle. To a prudent and cautious commander the way east offers very little prospect of success but a high probability of destruction, death and the loss of the legionary standards. In summary of the above points it can be said that, both strategically and tactically, for each eastwards step the Romans might have taken they would get weaker, while the Boudican rebels would get stronger.

Many of these aspects are necessarily supposition. However, there two pieces of literary evidence emphatically against an eastwards march. First, Tacitus says that Suetonius, “received into his army all those (civilians) who would go with him”¹⁶. Put simply, refugees do not voluntarily join an army that is deliberately marching into battle, they flee in the opposite direction, towards friendly lands and ports, nor does an army commander, who is deliberately seeking battle, encumber his small force with non-combatants. The second piece of literary evidence is that Tacitus tells us London was destroyed. Of course, this is also supported by the archaeological findings. For Suetonius to march eastwards towards the approaching horde and still for London to be destroyed is not impossible but would require some sort of flanking manoeuvre by the rebels to enable them to get behind Suetonius. Put simply, it is highly unlikely that an eastwards march by Suetonius would cause the rebel leaders to think that destroying London was more important than destroying Suetonius and his army. In conclusion it can be said with some confidence that Suetonius did not march eastwards.

To leave London by way of Watling Street, and a return to the north, may have been a less suicidal option but its likelihood as the route taken is outweighed by more negative than positive aspects. On the positive side would have been a move closer to the remains of the 9^th Legion with the prospects of some of its units joining Suetonius but, if this was possible then it might be supposed it would have done so while Suetonius was marching south to London. Another positive aspect is the general move back towards the military zone (roughly the area west of Icknield Street from Chester in the north, through Wroxeter and further southwards to Gloucester, Caerleon and finally Exeter, Fig.1). Such a move might have thrown off the following rebels, enabled Suetonius to regroup with units of the 14^th and 20^th Legions he had left in the military zone, before marching south, towards Gloucester, to join with the 2^nd Legion and then launch an eastwards directed campaign towards London along Ermin Street and the Portway (Fig.1). The negative aspects include the realisation that much of the above can be more readily accomplished by marching westwards out of London along the Portway, towards Silchester (Fig.1), and hence to the military zone. In further negation, the legionaries might have baulked at returning along a road where they knew they would be harassed again, where much of the stored supplies had already been consumed or destroyed during their southern march and to a final destination far from the 2^nd Legion in Exeter, the last whole legion which could come to their aid. Suetonius might have thought that many of the negative points against the eastwards route also apply to the northerly and that he would have to march with the Britons threatening his right flank unless the route was already blocked by the horde that destroyed the 9^th Legion and then followed him down Watling Street. What also might have weighed on Suetonius’ mind might have been the political effect of a northern march. For the Romans would have moved away from their oldest, firmest and most resolute allies among the British tribes, those south of the Thames, towards those more recently persuaded of Roman rule: Suetonius might have thought that the sight of a Roman army retreating northwards might have caused political upheaval in the northern tribes, possibly resulting in them attacking him in consort with the eastern tribes. Finally, the entrainment of the London civilians within his army strongly suggests, as it does for the eastern march and for the same reasons, that Suetonius marched either south, by crossing the Thames at London, or westwards towards Silchester.

To march south of the Thames would mean crossing the Roman bridges, probably located at a site near Westminster and in the modern London borough of Southwark, and then turning either east along Watling Street towards Canterbury and Richborough or south along Stane Street towards Chichester and the ports on the south coast (Fig. 1). If Suetonius crossed the bridges then he would probably have attempted to destroy them but, although generalised burning has been found at Southwark, no direct evidence for or against destruction of the bridges has yet been found. Not that the destruction of the bridges would have stopped the Britons crossing the Thames, as they had for millennia used fords and firm ground through the marshy estuary, probably in the vicinity of East Tilbury and possibly elsewhere¹⁷. In addition there were probably other bridges besides the Roman: for example, Cassius Dio, in his account of the later stages of the Battle of the Medway in 43AD, mentions that some Roman units pursued the retreating Britons across the Thames using a native bridge¹⁸. These other methods of crossing the Thames might have been used by the rebels prior to Suetonius leaving London, thereby blocking the routes south to safety, in which case he would have been forced to march west along the Portway. However, there is no archaeological evidence for this supposition. Assuming Suetonius did successfully cross the Thames then a turn to the east would lead to the safe havens of Richborough and Reculver, places where he could have rested for the winter, awaited reinforcements from Europe and then resumed his suppression of the revolt the following year. The negative consequences of this strategy might include: turning the south east of Britain (Kent etc.) into a conflict zone, thereby spreading the uprising to those areas most Romanized, and making the eventual reinforcing actions from Europe more difficult and costly; causing a more widespread uprising amongst the British tribes, as they realised that the Roman forces were split between Suetonius and the western military zone; the loss of many more Roman forts, settlements and lives as the rebels freely rampaged across much of Britain; the tribal force might have grown considerably by the following year necessitating the re-conquest of much of Britain; and Suetonius might have thought he would be replaced as Governor if he essentially retreated to somewhere like Richborough. Stane Street would have similar consequences, although Suetonius might have planned to turn westwards and strike towards the 2^nd Legion at Exeter. In favour of the Stane Street route is the large number of battle sites along the North and South Downs that match Tacitus’ description very well (Figs. 5 & 7). Finally, Tacitus’ account of the civilians marching with Suetonius is more credible if he turned south out of London, rather than eastwards or north along Watling Street.

Nevertheless, a southern escape from London is less likely than one to the west. For strategic reasons moving west from London into the western military zone, especially with the prospect of joining the 2^nd Legion, was far more favoured than any other route. Suetonius would have reunited his military forces in Britain, making it less likely he would have been replaced, and would not have endangered the south east of Britain, hence making the assistance from Europe at Richborough far more effective, together with the resultant pincer movement of his army marching from the west while the continental reinforcements marched east towards London. Essentially Suetonius would have retreated to a place of relative safety where, if necessary, he could pass the winter preparing for the next campaigning season, by his presence in the military zone dissuade the Welsh tribes from joining the rebellion and await the continental reinforcements.

For tactical reasons a march west out of London was also the most favoured. Taking the Portway to Silchester was the shortest and quickest route to the military zone and the all-important the 2^nd Legion. It passed through the land of Rome’s “most loyal”¹⁹ ally, the client king Cogidubnus of the Atrebates, whose capital was at Silchester [Calleva Atrebatum] and who might be relied upon to assist Suetonius and, at least, would have granted him free passage, safe from local harassment. Also, moving westwards would have placed the rebel forces in Suetonius’ wake, they would have been forced to follow as quickly as they could, which may, en masse, have been more slowly than the retreating Romans – not that this implies that units of tribesmen could not catch the Roman rear-guard and harass them.

Additionally, Silchester was, like London, a nexus of roads. Suetonius could have turned north towards Dorchester, or south-east towards the coast at Chichester, or south-south-west towards Winchester, or south-west towards Old Sarum, or north-west, along the Kennet Valley, towards either Cirencester and Gloucester or Mildenhall and Bath (Fig.6).

The Kennet river valley

The archaeological evidence is sparse and inconclusive for narrowing down the search for the battle site. Nicholas Fuentes identifies possible Boudican destruction evidence at three sites running roughly westwards from London: at Putney, Brentford and at Staines where the Portway crosses the Thames²⁰. He also puts forward Virginia Water (Fig. 5, and Table 1, number 37) as a possible battle site, it being the first location west of London and Staines to roughly match the terrain described by Tacitus. However, although this study lists the location as a possible battle site this is dependent on Nicholas Fuentes being correct in supposing that the Portway took a more southerly route (his Figure 2), across the Thames flood plain west of Staines. If the commonly accepted, more northerly route is correct then the battle site is flawed, the Romans being easily out-flanked amongst the shallow hills and valleys. From here the Portway proceeds westwards to Silchester.

In 2008 Michael Fulford, leader of the archaeological examinations being conducted at Silchester, announced²¹ that there was a significant episode of destruction between AD50 and AD75, followed by rebuilding along a 45 degree realignment of the urban plan. He tentatively linked the burning and destruction to the Boudican revolt but made it clear that there could be other explanations rather than the Boudican horde being directly responsible. Nevertheless, and applying all cautionary caveats, this is possibly an extremely important finding and would greatly assist this study in supporting Suetonius’ westwards march.

If Suetonius, his army and citizens from London, did arrive at Silchester then it was probable that the Roman commander would recommend an abandonment of the poorly-fortified town by Cogidubnus and his Atrebates, before the Boudican horde overran it. In which case, Suetonius might have preferred to take the road to Mildenhall and Bath, it keeping to lower, more easily-traversed terrain than other roads out of Silchester (Fig.6). This road would also have kept his force within the territory of the Atrebates rather than taking roads north or south that traversed respectively the less-friendly territories of the Dobunni and Belgae.

Figure 8: The Kennet river valley, possible battle sites (yellow dots) and Iron Age hill forts.

The question then arises how far from Silchester might he have marched? Did he owe protection to the citizens of Silchester? Could they march quickly towards Roman forts at, for example, Cirencester or did they take refuge in one of the old Iron Age forts in Berkshire? (Fig.8). And did this then mean Suetonius had to place his force between the citizens and the rebels?

These questions collectively suggest that time, energy, resources, armed support and kindly political will might have been rapidly diminishing, or in doubt, resulting in a battle site located quite close to Silchester – possibly only one or two day's march away. This makes the region of the Kennet river valley quite favourable for the site of Boudica's last battle. However, only time, some luck and/or systematic examination will reveal the actual battle site but hopefully this study’s examination of terrains, geographic features and the words of Tacitus will aid the hunt for the location which may be somewhere west, or north, of Silchester.

The battle

As always in this saga, the 2^nd Legion is tactically critical. For Suetonius to face and defeat the Boudican rebels that summer he might have thought he needed the 2^nd Legion and, as has already been mentioned, he may have earlier sent senior officers to take command of this recalcitrant unit and march it towards him. Possibly Suetonius had intended to combine his forces, commit them to battle and so destroy the rebel horde, rather than to over-winter in the military zone. But, something did not go to plan: maybe the civilians with Suetonius slowed him down too much; might his legionaries have been too tired after their exertions that summer (they had already marched 440km/275miles from Anglesey); possibly the Atrebates were not as friendly as he had hoped; Dio²² mentions that Suetonius was running short of supplies; maybe the harassing attacks by the following tribesmen were too severe, causing him to loose too many men; or, maybe, news reached Suetonius that the 2^nd Legion had not left Exeter after all or would not reach him in time. For whatever reason(s) Suetonius “prepared to break off delay and fight a battle”²³ with the surviving men of the 14^th and 20^th Legions marching with him.

Tacitus tells us indirectly that Suetonius had probably already identified the battle site long before it became necessary to use it. For example, the description of the battle site – a defile, approached by a plain and backed by a forest – is not suggestive of a site chosen in extremis, more likely one pre-selected by an experienced officer who had, while following one tactic, namely march west and join the 2^nd Legion, already thought of other contingencies and options. Having the battle site already in mind is not surprising when one considers the life of a Roman Governor, forever in the saddle, riding from one legionary inspection to yet another meeting with a client king, who relieves the boredom by examining the passing terrain, assessing its potential as a battle site and possibly using this pastime as an educational tool for his younger officers. Tacitus also mentions that, “there was not a soldier of the enemy in his front (battle line)”²⁴, suggesting that Suetonius had marched directly and rapidly to the site, possibly as an half-day quick march across country, sufficiently quickly to throw off the following rebels and outstrip any enemy flanking units and with sufficient time to rest his men, feed and water them and arrange his battle line before the Boudican rebels arrived and were themselves prepared for battle. Suetonius might have expected to have to wait for more than a day until the rebels had all gathered, together with “their wives riding in waggons, which they had placed on the extreme border of the plain”²⁵, and might have chosen a site where the water supply could be protected – probably requiring the defile to contain a substantial stream that flowed towards the rebel army.

Further indirect evidence of a premeditated battle plan is the realisation of how superior the terrain of the battle site was for Roman combat tactics and the situation Suetonius was in. Above all else he could not allow his legionaries to be out-flanked or, far worse still, surrounded. Nor, for the sake of morale, could his soldiers think that that event was probable. The legions were in a narrow defile, as already mentioned, probably about 1km wide, with rising ground at their sides where the lighter auxiliary and cavalry units could hold the flanks. The approach of the Britons to the Roman line was by a narrowing defile, forcing the horde of Britons to compress themselves, or limit the number of warriors and chariots engaging the Romans, thereby lessening their combat effectiveness. The Romans were probably at the top of a down-slope that favoured them in a charge by increasing their collision speed with the front rank of rebels. Above all else, the premeditated nature of the site is clearer when realising that it was a trap for the Britons, rather than just a refuge of last resort for the Romans. Suetonius had, in advance, chosen a battle site that appealed to the Britons; he had already reasoned that the Britons would think the Romans were trapped, in a weak position and ripe for destruction. Suetonius was, in choosing this superior terrain, inviting the Britons to attack because that would allow his men to control the battle once the Britons start their close approach, that was to launch waves of javelins at the compacted horde and then to charge, in compressed formation, at the Britons, driving them back with their shields before their swords stabbed and slashed the horde to destruction. To Suetonius, his officers and veterans, this outcome would be clear, but it was hidden from the Britons. In essence, Suetonius used his superior education, military training and combat experience to select a battle site, from among all those he had already seen on his travels, which allowed the best soldiers in the world to use their honed tactics to best effect and to hide her own destruction from Boudica’s eyes and mind.