Backs against the Wall, AD 117-113

In the early years of Hadrian’s reign, the military situation in Britain was in danger of spiralling out of control. The emperor hit on a radical solution, as Matthew Symonds describes.

This is Part Two of the special on Hadrian's Wall. You can read Part One here: Warfare & the Wall.

There are two ways of looking at Hadrian’s Wall. The first is as part of the network of frontier systems that girded the Roman Empire. During Hadrian’s reign, these stretched for roughly 13,000km through 20 modern countries on three continents. Set against that whole, the 117km length of Hadrian’s Wall looks pretty puny. But these frontier systems were not identical, and the Wall stands out from its peers by virtue of its scale. Take the linear barrier that was installed during Hadrian’s reign along the frontier in Upper Germany: a timber palisade, perhaps standing about 3m high. While this was still a stout obstacle, it is in a completely different league to the linear barriers that existed along Hadrian’s Wall. By the end of Hadrian’s reign, these comprised a ditch that averaged over 8m wide and 2.7m deep, a curtain wall probably rising roughly 4.3m to wall-walk height, and an enigmatic earthwork called the Vallum presenting a 36m-wide obstacle to the south. In places, spiky wooden obstacles festooned the berm between the ditch and curtain with the Roman equivalent of barbed wire.

A reconstruction of Hadrian’s Wall, showing work under way on installing spiky wooden obstacles between the ditch and curtain. The scale of Hadrian’s Wall makes it stand out from other Roman frontiers, raising the question of why this should be the case. Image: Tyne & Wear Archives & Museums.

As a formal frontier system of some kind is only to be expected in Britain – as elsewhere on the edges of empire – during this period, it has been proposed that the abnormal scale of the Wall is simply a flourish: a hollow piece of imperial rhetoric, serving no practical purpose beyond expressing the might of Rome. As we have seen, though, while the Britons appear ill equipped to hold their own against the Roman army in set-piece battles, they could inflict losses during hit-and-run attacks. The more dispersed military deployments visible in Wales, Scotland, and on the Tyne–Solway isthmus make sense as attempts to neutralise this threat. If so, it follows that efforts to counter British warriors were shaping military networks in the decades leading up to Hadrian’s visit. This brings us to the second way of viewing the Wall: as a control system whose design was a calculated response to the cocktail of violence served up in Britain during Hadrian’s reign.

Hadrian’s Wall is only one part of a wider network of frontier systems established on the edge of the Roman Empire. In Hadrian’s reign this network stretched for roughly 13,000km. Image: Dreamstime.

A link between warfare and the Wall is made explicit by the reconstructed text of a Roman inscription found at Jarrow. This probably once graced a victory monument and declared that ‘after the barbarians had been dispersed and the province of Britain had been recovered, he [presumably Hadrian] added a frontier line between either shore of the Ocean for 80 miles’. Taken at face value, this makes it plain that fighting formed the backdrop to the Wall’s origins. Yet, while there is abundant evidence for combat in Britain at around this time, we lack the details that the ancient literature furnishes for the Boudican revolt and Mons Graupius. Instead, events can only be loosely reconstructed by assembling a patchwork of different types of evidence. Drawing these threads together presents a picture of serious Roman troop losses. Our challenge is understanding the relationship between the military situation in Britain and the genesis of the Wall.

Resisting Rome

The statement in the Historia Augusta that the ‘Britons could not be kept under Roman sway’ at the beginning of Hadrian’s reign indicates that problems in the island can be traced back to 117. A letter written to the emperor Marcus Aurelius (r. 161-180) mentions notable Roman casualties in Britain, but provides no greater dating precision than them occurring while Hadrian was emperor. These snippets in the ancient histories are supported by information from surviving Roman inscriptions and coins. Vindolanda fort, which lies just south of the Wall, has produced a tombstone that appears to be Hadrianic and commemorates a centurion killed ‘in war’. A Roman coin issue featuring Britannia can be more closely dated to 119 or soon afterwards. It has long been suspected that these coins were minted after the turmoil noted in the Historia Augusta had been successfully suppressed. As the majority of these coins have been found in Britain, they may even represent part of a package of measures to help reconstruct a battered province.

Publius Aelius Hadrianus, the man we know as the emperor Hadrian. He reigned from 117-138 and was considered unconventional by contemporaries. In 122, Hadrian became only the second serving Roman emperor to visit Britain, where significant troop losses occurred during his reign. Map: courtesy of David J Breeze.

If so, the peace probably proved fleeting. Two more inscriptions reveal that an expeditio Britannica – that is, a military taskforce – was dispatched to the island with 3,000 legionary reinforcements during Hadrian’s reign. Surviving information about the career of one participant is hard to square with the taskforce making a contribution to fighting as early as 117-119. Instead, a date in the 120s is much more likely, which also fits with the use of the term expeditio. As the late Anthony Birley stressed, this normally indicates that an emperor was present in person. If the expeditio Britannica followed that rule, it can only have been dispatched in 122, when Hadrian was in Britain. The possibility that he arrived at the head of a taskforce helps illuminate his motivation to visit the island. It was also at around this time that a new legion – the VI Victrix – was transferred to Britain, meaning that more than 8,000 legionaries, presumably alongside an undisclosed number of auxiliaries, arrived in Britain in either the years around 122, or in 122 alone. The sudden need for this transfusion of fresh soldiers suggests a disaster of some magnitude.

Roman camps were built flanking a former hillfort at Burnswark. Here, one of those camps is visible in the left half of the photograph. From it, a hail of projectiles was unleashed on the hill summit, apparently as part of a Roman assault on the site. Image: John Reid.

These implications are matched by a set of bronze diplomas issued to veterans retiring from military service in Britain on 17 July 122. Such documents include a list of auxiliary units discharging soldiers on the day, and this particular example names 50 – a uniquely high number. One explanation for this exceptional quantity is that terms of service had been temporarily extended in order to quell a crisis. If so, by the time that the 17 July document was drawn up and the veterans discharged, the danger must have passed. On the face of it, this suggests a narrative whereby Hadrian and his taskforce achieve a notable victory after arriving in Britain, probably in April, when the Channel sailing season started. The stumbling block with this theory is that there is no hint in the surviving ancient accounts of Hadrian’s reign that he became embroiled in fighting while in Britain.

Hadrian’s Wall, as it would have appeared at the end of Hadrian’s reign. Its course closed off access to the lateral valley corridor on the Tyne– Solway isthmus from the north. Map: courtesy of David J Breeze.

Perhaps this omission simply means that the expeditio should be seen as a rare example that did not involve the emperor, and the taskforce sailed in a different year. But another explanation is possible. What we know of the Britons’ preferred tactics allows a speculative scenario for what happened to be sketched out. Given their greatest successes were achieved using surprise attacks, it seems most likely that the crisis commenced with Roman soldiers being ambushed while they were vulnerable, with isolated units perhaps being targeted in the aftermath. Here it is worth noting that the VI Victix legion came to Britain to replace the infamous Ninth or ‘lost’ Legion. This unit is last securely attested at its fortress in York in 107-108, and had disappeared from the Roman army list – presumably because it had been annihilated – by the 160s. Today, most specialists believe that the Ninth Legion was transferred out of Britain and met its fate in either Judaea or Parthia. Scholars such as Nick Hodgson, though, press the case for much of the legion being cut down in Britain. Roman losses on that kind of scale would certainly help to explain the number of reinforcements ferried to Britain.

A schematic representation of Hadrian’s Wall. (A) shows the original design, with a cordon of milecastles and turrets studding the curtain, while larger bases lay to the south on the Stanegate road. (B) shows how the plan was changed while construction was under way, adding thousands more soldiers in the Wall forts, and an earthwork to the south known as the Vallum.

Any link with the VI Victrix draws attention back to its arrival at some time around 122, and the merits of the expeditio occurring that year. In which case, perhaps the absence of accounts of Hadrian’s involvement in combat can be traced to another repeated theme found in the ancient literature: a general reluctance among British warriors to engage a prepared Roman army in pitched battle. A refusal to fight the Roman reinforcements would also explain why the best that the inscription fragment from Jarrow could credibly claim was that the ‘barbarians’ had been ‘dispersed’, rather than defeated or destroyed. If Hadrian did arrive with a taskforce, though, he surely coveted an outright victory. This brings to mind Callwell’s advice for regular soldiers trying to force elusive enemies to make a stand: threaten a town or shrine that they will feel compelled to defend.

An episode that fits with this approach played out at Burnswark, to the north of the Solway in south-west Scotland. There, a former hillfort is still held in a vice-like grip by two Roman camps. For many years, a scholarly dispute raged about whether these fortifications are the relics of a full-blooded Roman siege or a training facility set up to teach soldiers siege warfare. One objection to the real siege theory is that such a method was unnecessary, as the hilltop is sufficiently accessible to be stormed with relative ease. This problem disappears if one objective was to draw out an enemy force by threatening the settlement. By that scenario, taking the time to advertise Roman intentions would have been essential. Recent fieldwork led by John Reid suggests that Burnswark was indeed on the receiving end of a Roman assault, mounted after defenders were suppressed by a lethal hail of projectiles, including lead slingshot, launched from the siege camps. As this event can be broadly dated to the reigns of either Hadrian or his successor Antoninus Pius (r. 138-161), it is entirely possible that the attack was a Roman attempt to make its foes stand and fight. If it was associated with Hadrian’s presence, presumably this gambit failed and the emperor was unwilling to spend an entire season in Britain replicating the techniques that Agricola had resorted to in order to incite a battle at Mons Graupius.

Projecting a regular spacing system on to irregular terrain could produce absurdities. This milecastle, on Cawfields Crags, was built on a steep slope, facing an even steeper slope, adjacent to a pass on level ground.

Drawing a line

Where, then, does the Wall slot into this tentative timeline? The Historia Augusta implies that Hadrian ordered construction while he was in Britain, placing initial work in the aftermath of the proposed 122 expeditio. This seemingly finds support in the 17 July diplomas, which note the recent arrival of a new Roman governor of Britain: Aulus Platorius Nepos. His name also appears on numerous building inscriptions from the Wall, proving that work was well under way before Nepos’ tenure expired, by August 127 at the latest. Recently, though, a growing number of Wall scholars have followed Erik Graafstal’s lead and toyed with the idea that building work began before 122. This is in part because what we know of Hadrian’s character leaves no doubt that he would relish inspecting the works in person. But it also relates to a building inscription from one Wall post that does not name Nepos, or any other governor. Given Nepos’ fondness for appearing on such dedications, and given that construction of the post in question started very early in the building programme, this has raised suspicions that it was erected before Nepos arrived in Britain. If so, building was most likely under way in 121. Allowing a year or two for planning, surveying, clearance, troop movements, and logistics would point to a decision having been taken around 119: an excellent fit with the close of a first phase of Hadrianic hostilities in Britain.

This turret was moved an unusually long way from its measured location, allowing its garrison to control a narrow defile leading through the crags.

The fabric of the frontier could also help us understand how it fits into the wider military situation. Hadrian’s Wall was positioned to shut off access from the north to the natural east–west valley corridor on the Tyne–Solway isthmus. Initially, the Wall line was secured with a cordon of comparatively weakly manned installations known as milecastles and turrets. As you would expect, milecastles were positioned at intervals of approximately one Roman mile (1,479m). Most of these posts incorporated gateways allowing passage through Hadrian’s Wall, and also held modest garrisons, ranging from about eight to 32 soldiers. Turrets were erected between the milecastles at intervals of roughly a third of a Roman mile, resulting in a manned post every 495m or so along the curtain. As the soldiers on duty in the turrets were probably rotated out from the milecastles, an upper limit for the total number of men dispersed along the Wall line can be roughly estimated as 2,600. Together, they operated a surveillance system on a scale utterly unprecedented in Britain. Even so, positioning posts at set intervals marked a radical departure from the standard Roman practice of placing fortifications thoughtfully within the landscape in order to maximise their impact.

A gateway through the Wall. Most milecastles provided such passageways, placing a portal approximately every Roman mile along the Wall. Whether they were primarily intended for military or civilian use is key to establishing the likely impact of the Wall.

Unsurprisingly, imposing a regular spacing system on irregular terrain threw up some absurdities. One eye-catching example is a milecastle that was built on a steep slope, with its north gateway opening on to an even steeper slope, despite lying next to a pass on level ground. Such awkward arrangements are often taken as an example of the old military adage that you are not paid to think. Despite such inefficiencies, though, the profusion of posts appears well suited to minimise opportunities for infiltration by small groups, with subtle adjustments to the location of some installations even allowing them to sit more sensibly within the landscape. Surviving military documents from Egypt record Roman garrisons comparable to those in the milecastles tackling bands of 60 or so ‘barbarians’. Much larger enemy forces, though, would need to be dealt with by auxiliary units occupying the Roman forts arranged along the Stanegate road, which lay to the south of the Wall.

After work on the Wall started there was a major change in plan that involved adding a series of forts to Hadrian’s Wall. This example, at Housesteads, would have been home to roughly 800 soldiers. Image: John Reid.

Understanding the impact of Hadrian’s Wall hinges on determining who could pass through the milecastle gateways. Initially, these presented the only passageways through the frontier, with the exception of two places where major highways crossed the curtain. A growing number of scholars see the milecastle gateways as primarily a measure to minimise the inconvenience that the Wall posed to military manoeuvring, rather than access points for civilian traffic. Instead, merchants and others wishing to venture north (or south) were probably normally limited to the major highway crossings. At present, there is only sparse evidence for objects originating to the north of the Wall reaching the Roman province, indicating that trade was not a major factor. As Paul Bidwell has noted, if civilians were not allowed to pass through the milecastles, the Wall would have presented a significant barrier to north–south movement in what had previously been open countryside. Long stretches of the Wall’s course ploughed through regions that had been home to populous farming communities for centuries. Unilaterally severing these pre-existing working, political, and religious landscapes threatened numerous livelihoods, raising the risk that this act of division could provoke a hostile backlash.

The Vallum at Cawfields. This extraordinary earthwork ran to the south of Hadrian’s Wall, and was normally about 36m wide. It would hinder attempts to ambush soldiers or supply trains using the corridor of ground between the Wall curtain and Vallum.

Just such a shift in the local security situation would explain why the Wall underwent a radical change in plan while construction was under way. This saw the penny-packet garrisons manning the milecastle and turret cordon augmented by a series of forts holding full-size auxiliary units, adding approximately 9,000 soldiers to the immediate vicinity of the Wall line. In places, existing milecastles and turrets had to be levelled to make way for these new bases. Many of the forts were built astride the Wall curtain, resulting in three of the four main gateways opening to the north, allowing their units to deploy rapidly in that direction. Problems to the south are also indicated by the addition of the Vallum earthwork behind the curtain, a feature that is without parallel on any other Roman frontier. This arrangement created a secure corridor of land between the Wall curtain and Vallum, where it would be very difficult to spring ambushes on soldiers, supply trains, or other traffic.

Changing circumstances

Comparing the capabilities of these two versions of the Wall suggests that this bold revision to the plan followed a step-change in the nature of resistance. The milecastle and turret cordon makes most sense as a means to deter or detect and destroy attempts by relatively small groups to cross the Wall line. While such limited numbers of soldiers could not stop full-blown armies, they would make a valuable contribution to attempts to stamp out guerrilla warfare within the Roman province. It would be hard for small bands of warriors to cross the Wall and move in and out of the province at will, denying them opportunities to benefit from safe havens or support available beyond the sphere of Roman control. Any mounted Britons seeking to cross illicitly would have to choose between abandoning their steeds or capturing a gateway. As such, the initial plan for the Wall appears well calibrated to suppress a way of war that the Britons excelled at.

The Wall and Castle Nick milecastle. Once operational, the frontier would have posed a considerable obstacle to movement through the region, especially if the milecastle gateways were normally reserved for military use. Image: John Reid.

It is probably this need, coupled with the large pre-existing population numbers in the vicinity of the Tyne–Solway isthmus, that explains the difference in scale between the Roman frontiers in Germany and Britain. The presence of sizable farming communities also meant, though, that building the Wall risked destabilising a traditional way of life for thousands – and probably tens of thousands – of local people living near the isthmus. That the threat the Wall posed to countless everyday local interests spurred resistance is implied by the abrupt need for the forts and Vallum. As the forts faced north and the Vallum south, this suggests problems to both the front and rear. Equally, the thousands of soldiers making up the auxiliary units housed in the forts added an ability to project concentrated military strike-power to a system that originally seems – as David Breeze and the late Brian Dobson observed – geared towards controlling north–south movement.

If the initial plan for the Wall was drawn up after the cessation of disturbances in 117-119, it makes sense as an innovative measure to frustrate guerrilla warfare and improve security within the Roman province. A relatively rapid need to rethink the basic Wall blueprint, though, suggests that the very act of building it galvanised resistance. The wealth of evidence for a major Roman military response to a problem in Britain at around this time has already been set out. Perhaps, then, the Wall itself is the missing piece of the jigsaw for puzzling out how and why events may have come to a head in 122: Hadrian and the expeditio Britannica arrived 1,900 years ago because imposing a monumental barrier system as a solution to provincial security had unleashed an orgy of violence. •

Matthew Symonds is the author of Hadrian’s Wall: creating division (Bloomsbury, 2021).
All images: M Symonds, unless otherwise stated.