Hadrian's Imaginary Border Wall - That Didn't Work

Imaginary Walls

In AD 122, Emperor Hadrian’s first Imperial tour brought him to the Roman province of Britannia, and more specifically its Northern Border.  Here he imagined a great stone wall from sea to shining sea built by his army with the support of the Native population; what he got was a complete disaster.

This is not the Wall that Hadrian or later generations imagined; the evidence for the failure of this policy has been lost in our simplistic picture of this largely non-existent monument and more generally in our admiration of the Romans.

As the most politically powerful politician in the West, he could not only order and fund its construction, but he could also insist that the Natives cooperate in helping wall themselves off from the rest of the Island.   While on level it can be seen as autocratic gesture politics, a very physical symbol of Hadrian’s new policy of territorial and cultural consolidation, it was also an attempt to solve a very real border security issue. 

The Wall is largely an imaginary thing; about 10% has survived in some consolidated form, and while it is not unimpressive in its setting, you have to mostly make it up above waist high.   Despite this, it has lived large in our collective imagination as an artist’s impression, with its own tradition of visual representation.

However, the Wall was a real engineering project, so it can be modelled mathematically in terms of its logistics, planning and execution. What the numbers and archaeology imply is that the project failed, catastrophically, and within a couple of years the wheels had come off this Emperor's plans to build a border wall.

Metanarratives.

"Walls work....”

“They say 'a wall is medieval.' Well, so is a wheel. A wheel is older than a wall.“

President Donald J Trump, Jan 2019

The past has always been subject to political and cultural misappropriation, it is perhaps why we need to invent it.  However, the recent assertion on the nature of Walls represents a remarkable challenge to the accepted norms of education, rationality and intelligence in an executive skill set. While it might be considered politically incorrect to mock such disability, I would be failing in my responsibility as a structural archaeologist not to fact-check this particular missive, as well as celebrate more generally this remarkable historical nadir in administrative competency and political duplicity.

However, much as it tempting to try and draw parallels with current politics, particularly with the USA, any superficial correspondence is mainly derived from the use of similar terms.   The Romans had no concept of self-governance by anyone and for anyone except as it applied to the relatively small and restricted gene pool of the senatorial class.   This Roman aristocracy had accepted necessity of autocracy, but importantly, among a self-selecting group, it was a meritocracy that ensured a degree of competence and experience in its officials, particularly its chief executive officer.

Cognitive Dissonance.

Even though all representations of Hadrian's Wall are imaginary, this idea of failure probably  conflicts with our picture of a great stone Wall from sea to shining sea, as well as our general positive view of Roman achievement.

Primarily through religion and the remarkable persistence of Latin literacy, The Romans have been woven so deeply into the fabric of Western Culture that we no longer perceive the joins.  Notably, they are the fall-back cultural reference to invoke ideas of power, strength, authority, stability and order.  The Romans were part of our childhood; they had a walk on part in the bible, and usually form one of our earliest educational explorations of History.

This is a pictorial world, from the quaint anachronisms of medieval stained glass to the pulsating classical re-imaginings of Hollywood our culture has sought and consumed a visual past.  Much of our cultures fictional world exists in the past where it merges with whatever actuality is understood at the time.  It’s the past’s self-serving plasticity that drives much of our culture, and it is against this composite magical, heroic, romantic, self-propagating backdrop of our collective imagination that archaeologists must attempt to function.

Importantly, our Latin based classical world existed long before the advent of Archaeology, and as a consequence, excavation data has often been approached from the perspective of an existing literary tradition.  Thus, for many reasons, the dark secret of this failure had long been beyond the imagination of classical scholarship, but the archaeology tells a different story.

The Wall as numbers

The essential difference between imagining or drawing a structure and actually building a real one is Maths. Using numbers is the principle tool of abstraction by which engineers implicitly or explicitly create, plan and execute a successful design.  Given the simplicity of the concept of a mortared stone wall, albeit a “New technology” in this context, apart from the bridges, the project is mainly a problem of logistics. The central idea of Theoretical Structural Archaeology is that engineered structures can be modelled mathematically; this has the additional advantage of not approaching the archaeological evidence from a pictorial or literary perspective. 

My current understanding of the structural evidence is based on new mathematical modelling, which strongly suggests the narrative summarised below and fully justifies the characterisation of the project as a disaster

Hadrian’s Backstory; A Senatorial Class act

Broadly, by the time of Hadrian, real political power in Rome still rested with the 600 senators, even though since Augustus, one of their numbers was chosen to be Emperor.  [There was no written constitution, and the central issue of Roman political history would remain exactly how the process of ‘choosing’ should work].

This self-selecting ruling elite, while living a life of extraordinary privilege, were expected to serve the state, having carefully tailored paid political careers that took them through the army, Law, and administration, even religion, and back again.  An emperor like Hadrian had been a judge, army officer, treasury official, legionary commander, provincial governor, as well as a Consul, one of the two vestigial republican heads of state elected annually.  It is a measure of the stability of the constitutional settlement that Hadrian, who was Consul three times, could also hold one of these offices while also being Emperor.  Therefore it should be understood that the Emperor in this period was a constitutional figure, with specific responsibility and powers.   As Commander in Chief of a standing army of about 250,000 men, his particular role was security, more especially in those provinces of the empire that required a garrison. 

His Biographers assert that Hadrian pursued peace as aggressively as his predecessor Trajan had pursued war.  Trajan’s profitable wars in Dacia had yielded serious amounts of bullion and slaves, however, more recent military adventurism in Iraq had been a disaster, destabilising the region.  As well as problems in the East, Hadrian also seems to have inherited trouble on Western edge of the empire, where in Britain, the army had abandoned Southern and Eastern Scotland, falling back to northern England, where they may have suffered further reverses while Trajan’s attention was elsewhere

Ruling Britannia

Hadrian was the first emperor to visit the Island since Claudius came to celebrate his 'conquest' of Britain nearly eighty years earlier.  The intervening period had seeing a slow and often ineffectual attempt to gain control of the whole island, such that by Hadrian’s time territorial ambitions were restricted to the southern half.

While this represented between 3-4 % of the empire, the loyalty and security of the population was ensured by the presence of 13% of the empire’s troops in the province.  In return for their protection, the natives would have been expected to be provided much of the food and presumably other materials to supply the largest provincial army of occupation anywhere in the Empire.  

The degree to which the Romans had successfully integrated the traditional aristocracies into their own social hierarchy and culture is unclear.  For Hadrian Romanisation was a part of his mission of bringing peace and prosperity, so in addition to commissioning the Wall, he also initiated the development of a new Forum in London, which by this stage had taken over as the governmental and logistical hub for the administration of the Island. 

His coins are the first to have Britannia personified on the reverse, albeit with her head in her hands in a gesture of sorrow or mourning, reminiscent of Dacian coins after Trajan had finished with them.  While not a very auspicious start, it was perhaps appropriate, given that within a few years, London would be burnt, and the Bronze statue commemorating Hadrian’s visit taken from the Forum, smashed and thrown in the Thames.

Why a wall

The strategy of building a Wall adopted by Hadrian was a novel, untried, time consuming and expensive; it was only made possible by the presence of limestone along most of the frontier.

Given that the resources of the Emperor with his court were backing this revolutionary project, we have to assume that the Wall had been planned and costed, presumably to be finished during the governorship of Nepos, i.e. about five years, ending around AD127.  This New Governor of Britain was an important member of Team Hadrian, who had been co-consul with the Emperor, and importantly, he had supervised infrastructure projects for Trajan.

The Wall was piece of military infrastructure, built and manned by the army, which offered a solution to a real security issue.  Put simply; while infantry can climb the Wall, without baggage in the form of pack animals or wheeled transport, and lacking cavalry support, they cannot offer significant threat to the important economic assets further south.  

Viewed from the North, it is equally simple; the objective is to capture a gate, and with one every mile, there were plenty to choose from.

However, even a generous reading of the Romans' intentions would envision a garrison of century per mile, with 40 men in each milecastle and the rest back at one of the forts.   Split that into 3 watches, and we have little more than a dozen men manning two gates, a pair of turrets, and guarding a mile of Wall.  This might challenge many people's vision of the wall with frequent patrols of soldiers marching back and forth ready to fight off disparate groups of attackers trying to climb the Wall; this works for legionary fortress with roughly one man per foot of perimeter, but with less than one man per 100 foot it’s a non-starter.

To put that in perspective, in the only documented major battle against the Highlanders, the Battle of Mons Graupius in 84, the Romans had reportedly defeated a force of around 30,000.  The basic units of auxiliary army units manning the wall are cohorts of 600 men, perhaps up to 1000 when supplemented by cavalry, occupying forts about 7 miles apart, so no milecastle should be much more than an hour from infantry reinforcement.

In theory, the multiple gates give the defenders the counter-attacking options which are typical of a Roman fort, with the prospect of trapping the enemy against the Wall.  However, the nearest Legionary forces were based some hundred miles and several days march to the south, and the garrison alone would find it difficult to concentrate while also maintaining its commitments to manning the Wall’s many fixed positions.

Thus, the Wall can only work if there is sufficient warning of an attack to allow reinforcement of the relevant sections and the pre-positioning appropriate resources.  Without good intelligence, the enemy can turn up in force unexpectedly, or outflank the frontier using the Sea, in which case the strategic situation could deteriorate very quickly for the defenders.  The previous border was more typical, with a series of forts linked by a road; presumably this had proved too porous, with hostile forces passing undetected through this screen, resulting in sufficient military loss to prompt such a radical and expensive solution.

As a consequence, Hadrian’ decision to build his Wall is an important insight into the political situation at the time.  It is simply not realistic to imagine that the territory north of the Wall, immediately adjacent to the largest military garrison in the Empire, was anything other than cooperative and acting as a buffer against hostile elements further north.  The whole plan is rendered ineffectual if the buffer state fails to prevent or at least warn of a direct attack in force on the Wall, and catastrophic if this occurs during construction.

The building of Hadrian’s Wall 122-138

"Hadrian travelled through one province after another…. inspecting all the garrisons and forts. Some of these he removed to more desirable places, some he abolished, and he also established some new ones." [Cassius Dio 9.1].

In 122, when Hadrian and his court came to Britain, the garrison had been reinforced by the arrival of Legion VI along with the New Governor from Germany; Nepos, a close personal friend of the emperor.  These latter two events, particularly the appointment of Nepos, suggest that the decision to construct a permanent frontier had already been taken. 

In this first season an initial frontier was constructed from the bridgehead at Newcastle to the Cumbrian Coast comprising a standard timber rampart with a ditch in front.  Constructed by the army operating across the width of the country, and because this was effectively an extended fort perimeter with gates every mile and intervening turrets, typical of legionary field works, it could be accomplished relatively quickly.  This timber frontier was laid out to the same fixed scheme as the Stone Wall that was to replace it.  The route cuts more or less straight across the narrowest part of the country, along a line designed to take advantage of the spectacular escarpment of the Whin Sill.

Presumably, under the personal direction of the emperor, a series of elaborate forts, with three double gates opening north of the Wall, were laid out along the line, supplementing some of the existing ones from the earlier frontier. 

Work in this early phase was characterised by an abundance of unskilled labour evidenced by the digging of a construction trench for a frontier road, [The Vallum].  This was unnecessary, even counterproductive at this stage, unless there was a surplus of unskilled labour with nothing better to do towards the building of the Wall.  The excavation of a channel to divert the North Tyne at Chollerton in preparation for the building of the Bridge, as well as the digging of Wall foundation trenches considerably in advance of construction may also be part of this pattern.

In addition to the significant amount of planning and preparation work required for the replacement of the frontier in stone, a crucial logistical constraint was the availability of lime mortar.  The amount of dried fire wood required is equal to the weight of lime produced, so unless coal was used, there was a lead time to the production of mortar that takes the process into the next season [123] before building proper could start.  From then on, as sections of the stone frontier are completed, recycled wood from the timber rampart also becomes available for use as fuel or for building work.  

In this first season the army would have to build a series of more typical temporary forts to house the garrison and workforce close to the works, probably comprising a small camp every mile with larger camps reflecting the distribution of forts.

In 123 work on the Wall began in earnest with the army concentrated in the east along a 62km section, working on the complex aspects simultaneously, with aim of completing the Wall progressively in a westward direction.   Unlike the west, the eastern side of the country had abundant limestone, but it was also strategically stronger, being much better served by the navy and close to legionary hub at York.

In this second season, work on the most complex and time consuming tasks was prioritised, notably building the three bridges, three new forts, and the milecastles with their arched gateways.  The construction of the milecastles served to develop the logistic network, ensuring that quarrying and lime mortar production has to been established all along the route as far as the Bridge at Willowford.

The secondary priority was joining up these fixed units with a 10 feet thick curtain wall of mortared sandstone blocks on a pre-prepared foundation, known to have been organised around individual centuries. 

In this second season, the construction of a road did not progress, perhaps it was scheduled to start in year 3, but manpower could to be issue.  Just as it only makes sense to dig a foundation if there is a surplus of labour, similarly, only a shortage would prevent the next obvious step of completing the road in tandem with Wall, utilising the same resources.  It is the decisions around this aspect of the project are the key to what happened next.

Progress was halted, probably in the 124 season; it seems probable that there was a serious revolt in Southern England, evidenced by the destruction of Roman London, an intriguing spread of skulls in the area, the building of a new fort, and the sending of significant Legionary reinforcements from the continent. Whatever the army was doing, it was not progressing work on the Wall.

An analysis of the curtain Wall Logistics, suggests that the Romans suffered a significant loss of manpower, skills, and perhaps other logistical assets during the second part of Nepos governorship.  This resulted in a new plan under governor Germanus, abandoning or postponing the plan for the road and scaling back the Curtain Wall to 8’ or less.  Notably, the addition of three extra forts in the central sector strongly suggest the initial plan had left this area lightly defended relying on the topography of the Whin Sill escarpment and existing forts at Vindolanda and Carvoran .  The Wall was also extended from Newcastle to Wallsend, indicating that another potential weakness had been exposed.

However, this Narrow Wall plan was also never completed, so it is possible that both the eastward extension and the extra forts may reflect serious incursions from the North during the execution of this second plan.  

It is unclear how far work had progressed when Germanus was replaced by Severus, but it is known that he was reputedly Rome’s top general, because he was summon from Britain to deal with a serious revolt in Judea in 133. 

Progress was so slow that the timber rampart west of the fort Birdoswald, made of alder and hazel, and was too badly rotted be functional or recycled.  As a result new temporary ramparts were built to allow the work to continue on the Wall to the North of the Original line. 

Sisenna was the fourth Governor in charge of the project when Hadrian died in 138, but despite significant scaling back and the sending of additional troops progress towards the replacement of the frontier in stone had reached around roman mile 56 of 80.  The project seems to have met its ignominious end just 7 miles beyond where the army had been building their Broad Wall Bridge at Willowford 15 years earlier. 

An Imperfect Subjunctive Past

“… the first to construct a wall, eighty miles in length, which was to separate the barbarians from the Romans”.  [Historia Augusta].

This is the only significant reference to Hadrian’s Wall; it is hardly a celebration or ringing endorsement of a foreign policy triumph, and the Latin carries the implicit meaning that it failed in its purpose; {………., qui barbaros Romanosque divideret. }.

Hadrian had no doubt assumed that the population of Southern England would be prepared to participate by providing labour and other resources in addition to supporting the largest army of occupation in the empire. Presumably, the “Normal” distribution of this large garrison represented a response to existing security concerns.  

The stress on the labour supply has implications for the food production, something easily upset by external factors such as the weather.  However, the biggest risk is the actual project itself, which required the disposition of the army along a 73 mile frontier, in a manner best suited to the needs of construction.

One of the most frequent causes of military defeats is surprise, which almost by definition is being caught with your forces improperly disposed; [such as being ambushed while marching in column]. Geographically, it’s a position that can be easily outflanked by sea, and, as already noted, the entire strategy hinges on the allegiance and effectiveness of the buffer state to the north. Taking defensive position hands the initiative to the enemy, in particular the ability to concentrate at perceived points of weakness, which ironically, in this case, was probably the area, assumed to be most secure.

In addition, the project has the same logistical problems of supplying an army in the field, but without prospect of foraging supplies or booty as might be expected during a campaign.   The construction of a static line of defence combines most of the problems of campaigning with none of the advantages.

With the benefit of hindsight and in the light of subsequent modification, the plethora of gates would appear to have been a weakness, offering multiple potential breaches in the wall.  From Hadrian’s perspective, they must represent multiple places to counter-attack the enemy, since the strategic raison d'être has to assume there is time to pre-position sufficient forces to repel any attack. This reinforces the idea that the Wall can only conceivably serve any realistic military function as part of a wider political settlement involving the political allegiance and cooperation of the territory to the North.

Notably, the principle characteristic of subsequent development of the Wall, both in terms of the Milecastles and the Forts was the blocking of many of these gates.

Rationalising the irrational

“He personally viewed and investigated absolutely everything, not merely the usual appurtenances of camps, such as weapons, engines, trenches, ramparts and palisades, but also the private affairs of everyone, ……”[Cassius Dio 9.2]

Numbers only get you so far, in that engineering, particular military engineering is usually self-explanatory, and there is even an expectation of subtlety and ingenuity; but Hadrian’s Wall is dumb. Consider milecastle 39, on the top of the escarpment, with a set of gates opening onto precipitous drop, and it is obvious that Hadrian’s Wall is cookie cutter military architecture imposed on a landscape; it is an idea of a Wall; a back of the scroll sketch.

The multitude of gates is symptomatic of deeper problem about the design and execution of the project; this is not the work of a professional or competent commander in the field, but a simplistic and risky idea rigidly enforced by executive order.  The irrationality of the archaeological evidence can only be explained by seeking reasons in vagaries of Roman History, in particular the portrayal of Hadrian's character of in the two main biographical sources.

While, as emperors go, Hadrian was seen as a good bloke, a constitutional team player, he was also self-opinionated and more than a little contrary.  He had a high regard for own ability in all matters, certainly as it pertained to being Emperor and Commander-in-chief; he was hands on, nosy, meddlesome and got intimately involved in all aspects of military affairs. 

While it is easy to be drawn into the often prejudicial rabbit holes left by his biographers, Cassius Dio goes to some length to explain the story of Apollodorus, Trajan’s architect, who had Hadrian had banished and then killed.  Apparently, he criticised Hadrian’s knowledge of architecture in his youth, and then had been honest about the technical shortcomings of a design of a Temple proposed by the newly minted Emperor; this failure by a social inferior to take the opportunity to flatter the emperor was his downfall.

Thus, while Roman Senators like Hadrian were exceptionally well educated and uniquely experienced in administration, they were not all equally adept at adapting local talents to their needs.   Trajan did not fancy himself as an architect, and utilised professional talent like Apollodorus to design his bridges, whereas Hadrian would be tempted to do it himself, putting those involved in a difficult and potentially perilous position.

It almost feels like a stereotype; an arrogant emperor making sweeping decisions without adequate preparations, attention to detail and thought of consequences, but it almost exactly mirrors the criticism levelled against Hadrian by the unfortunate Apollodorus.

Pax Romana

Hadrian never returned to Britain, and the province hardly troubles his biographers further, and more generally only one episode clouds the otherwise sunny reputation of his reign.

In 130 Hadrian had visited Jerusalem, which had been destroyed by the Romans in 69, and decided to rebuild it as a Pagan Roman city;

"At Jerusalem Hadrian founded a city in place of the one which had been razed to the ground, naming it Aelia Capitolina…. This brought on a war of no slight importance nor of brief duration. . . . .

. . . . . . . . . . . . . .. . . . . .. . . . . . .   Few Jews survived. Fifty of their most important fortresses and 985 of their better-known villages were razed to the ground. 580,000 were killed…. As for the numbers who perished from starvation, disease, or fires, that was impossible to establish."   

Cassius Dio, The Roman History, 69.12.1, & 69.14.3

The reason for this digression is firstly, that it was the Governor Severus that Hadrian summoned from Britain to deal with this Revolt, and secondly, in a famous quote, an author likened the situation in Britain to the Jewish War documented above.

“... under the rule of your grandfather Hadrian what a number of soldiers were killed by the Jews, what a number by the Britons”

Marcus Cornelius Fronto, letter to Marcus Aurelius, AD162

This is the only direct reference to serious military losses in Britain, however, that the Romans suffered a significant loss of manpower, skills, and perhaps other assets during the project is evident from the numbers.  Only two thirds of the Hadrian’s Wall was ever built; despite being dramatically scaled back, what probably started as a 5 year project, was abandoned unfinished after 16 years by his successor.

The permanence of mortared stone construction is clearly a statement about the political solution this Wall represents; the Emperor had solved a troublesome problem in perpetuity, and made a statement about the limits of Roman territorial interest.   There is an eerie parallel, in that, two years after an imperial visit, the policy decisions taken have precipitated a crisis in the region; in both cases, Roman losses are hinted at, but in this case the response is documented.  For an emperor and 600 hundred of his peers to maintain control over 60 million people, no effort could be spared in punitive responses against sedition. 

Just to be clear; Hadrian was a Good Emperor, widely admired, he had respected the constitutional norms and very few of his fellow senators had died at his hands.  For his biographers, his reported killing of the architect Apollodorus of Damascus out of jealousy was regarded as a character flaw, and his genocide of the Jews was footnote in History.

Importantly, History has noted Hadrian’s complete self-confidence in his own abilities and knowledge in all matters, which combined with absolute military power, does much to explain the Wall.  Autocrats don’t have to admit they were wrong, and their contemporaries would be unwise to suggest it; it is clear that Hadrian blamed Nepos for the initial failure, and he never held office again.

More modern narratives of the Wall have stressed the idea of ‘dislocations’ or disruptions in the building program due to warfare, with Roman losses evident, although little thought has been given to the native population, or the role that this construction projects played in this cycle of violence.

End Game

The actions of the new emperor, Antoninus Pius, in reoccupying southern Scotland and building a new shorter wall across the Forth - Clyde Isthmus, tell us much about the failure of Hadrian’s frontier. It was considered preferable to build a new 63 km structure further north than complete the remaining 35 km; Hadrian’s Wall had not solved the problem, and the political alliance to the North had failed to protect his project. 

Like many extraordinary military adventures driven by the character of a commander in chief, ironically, it was probably Hadrian’s over-involvement that contributed to the failure of his own idea.

Notwithstanding the technical failings of the design, what remains of the Broad Wall attests to the logistical feasibility of the project, suggesting that this was a failure of politics not engineering.  Modelled as a logistical process, “building” the Wall was only the last stage in a series of labour intensive procedures which even with 3 legions and auxiliaries, would be unrealistic without significant additional manpower resources.   It is this unskilled labour that is harder to account for, but the failure of the plans has left a valuable snapshot in the archaeology, particularly the failure to complete a road clearly considered feasible at the outset.          

By the end of the century, some form of frontier Wall was functioning, although in very different circumstances; notably, most of the gates had been blocked.  More broadly, a tight grip was maintained over the Northern approaches to the Wall, and the vulnerable western flank along the Cumbrian Coast was consolidated.

However, one of most significant changes is the appearance of building inscriptions celebrating the contributions of corvée or civilian work parties, a marked change from the exclusively Military ones from Hadrian’s reign.   It would appear that by the end of the century, Hadrian’s vision of a Wall to “separate the barbarians from the Romans” had become politically relevant to the people living south of the Wall.  Thus, fifty years or more since Hadrian first imagined his Wall, one is actually finished as a complete stone border wall, and starts to function as we might imagine; this is the Wall that the tourists visit.

The North - South dynamic would remain a security issue for another 1500 years, and its politics persist today, reminding us that Hadrian’s border wall was a passing fad, a costly folly, which nevertheless successful fuelled the imagination of future generations in many unexpected ways.