Hadrian's Wall: when and why was it built? A brief guide

Whilst this has been justly labelled overkill, it does seem that the northern British tribes were troublesome. Wars in Britain are mentioned so frequently in literary sources that some archaeologists accuse the ancient authors of exaggeration. In truth, the British tribes did not readily accept Romanisation. They continued to farm the land in their old ways, and probably fought each other. We do not know enough about the tribes and their organisation to be certain that they were not perpetually aggressive, which in turn means that the function of Hadrian’s Wall can be interpreted only from the archaeological remains, with no clues as to Roman policy in dealing with natives.

• Jump to | Highlights of Hadrian's Wall

How many forts made up the wall?

The frontier system was complex. Starting from the north and working south, there were outposts beyond the wall, three Hadrianic forts in the west, and later forts in the east along what is now the A68 (a major road running from Darlington to Edinburgh). The original version of the wall in the west, from the river Irthing to the Solway Firth, was built of turf.

It could be that the tribes in this area were hostile, and the frontier had to be built rapidly. On the other hand, there could have been a shortage of suitable stone, since the locally available red sandstone is too friable, or easily crumbled. This western section of the wall was replaced in better stone in the second century.

The soldiers in the outposts may have undertaken regular patrols to observe the natives, as suggested by the names of some of the third-century units called ‘exploratores’, or scouts.

Further south there was the wall itself. It was protected by a ditch on its northern side, designed to prevent close approach, and reinforced in some places by three rows of pits, probably containing stacked thorn branches, which made penetration difficult. These features may have been established in the flatter areas, perhaps not all along the wall.

• Listen | Historian Rob Collins answers the big questions on Britain’s most famous Roman fortification. He explores the boundary’s creation and purpose, as well as everyday life on the wall.

How tall was Hadrian's Wall?

Then came the wall itself, originally around ten Roman feet [shorter than standard English feet] thick, later reduced to eight feet, resulting in a frontier of different dimensions. We do not know how high it was, and most controversially there may or may not have been a wall-walk along the top. No one can say if the Romans patrolled along the wall or confined their lookout posts to the forts, fortlets called ‘milecastles’, and turrets placed every third of a mile between them.

Whether or not there was a wall-walk, there is still a lot of dead ground where observation would be impeded. However, this probably did not matter, as it is unlikely that the wall would be defended like a castle under siege. Instead, the most probable function of the wall was to prevent anyone from getting too close or massing together in the distance. However, it has been suggested that manning the wall top would serve to delay hostile natives, while troops were assembled.

South of the wall there was another, larger ditch, labelled the ‘vallum’ by the venerable Bede (although, to the Romans, that term referred to the whole frontier system). On either side of this ditch there was a mound of earth. The vallum is a puzzle, variously interpreted by archaeologists. It was clearly important to the Romans because – unlike the northern ditch – it was continuous, and cut through rock where necessary. It is possible that the tribes south of the wall were prone to raiding. This may be the reason why the Roman dug the vallum – in order to guard vehicles and animals belonging to the forts.

How effective was Hadrian's Wall as a barrier?

No Roman frontier would have been capable of stopping masses of tribesmen who were determined to cross it. However, the presence of a solid barrier backed up with military force provided a strong psychological deterrent. It is significant that the emperors who followed Hadrian did not abandon the concept of running barriers. Instead they repaired and rebuilt frontiers. For reasons that archaeologists do not fully understand, Hadrian’s successor, Antoninus Pius, took over Lowland Scotland and built a similar frontier of turf between the Forth and the Clyde. However, it was held for only about two decades before Hadrian’s Wall was recommissioned and remained the northern frontier of the province of Britannia (even though military campaigns were undertaken to the north of it).

In the early third century the emperor Severus fought a war in Scotland, but did not hold the territory. He repaired Hadrian’s Wall so extensively that 19th-century archaeologists believed that he had built it. A century later, when Constantius Chlorus also campaigned in the north, Hadrian’s Wall remained the frontier line. No one can say why these emperors did not annexe the lands that they fought over.

What happened to the wall at the end of the Roman period is not entirely clear. Its function as a frontier may have been lost, with people instead trying to make a living inside the forts, looking to their own protection for as long as they could. Parts of the wall were repaired in timber or occasionally crude stonework, but the infrastructure of the empire had lost cohesion. By the late sixth century, much of the frontier had probably been abandoned.

The fact that we do not know everything there is to know about the wall is part of its fascination. Furthermore, on top of its historical interest, the wall also runs through some of the most stunning scenery in northern England.

Patricia Southern is the author of Hadrian’s Wall: Everyday Life on a Roman Frontier (Amberley, 2016)

Highlights of Hadrian's Wall

Julian Richards, archaeologist, broadcaster and writer, presents six highlights of the structure…

Housesteads (Vercovicium)

Of all the forts on Hadrian’s Wall, Housesteads has the most dramatic setting. There are well-preserved buildings, including granaries, a hospital, barracks, commanders’ house and latrines. It’s amazing to think of the variety of languages that would have been heard there, on the most northerly edge of the Empire. The north gate shows the ageless workings of the military mind. Although on a precipitous slope, the architect stuck rigidly to the standard plan and placed the gate in a most unsuitable location. This necessitated building an additional gate at Knag Burn, 300 metres east.

This is the place to do a bit of wall exploring. To the south are the remains of a civilian settlement, a reminder that it was more than just a military community. And, only a short walk to the west is the well-preserved milecastle 37 where the compulsory gate (wide enough for a cart) leads straight over a cliff (the military mind again).

Birdoswald (Banna)

The most westerly of the wall forts that survive well is in beautiful countryside overlooking the River Irthing. The east gate has the highest surviving masonry of any fort on the wall. Excavations have uncovered evidence of use continuing into the post-Roman period; a Roman granary was converted into a large hall, possibly in the fifth and sixth centuries AD. This is important for understanding the fate of Hadrian’s Wall. Such structures may have become the centres for descendants of the last garrison, who stayed after the collapse of the empire becoming something akin to a local militia. Possibly this happened at other forts but in many cases 18th- and 19th-century investigations have removed the evidence. Outside the fort geophysical survey has revealed a very large civilian settlement. A short walk to the east of Birdoswald leads to the remains of milecastle 49 (Harrow’s Scar) with dramatic views across the River Irthing and the remains of a bridge that carried the wall over the river.

Chesterholm (Vindolanda)

Vindolanda is one of the most remarkable and exciting military sites in Roman Britain. Located two miles south of Hadrian’s Wall, the visible remains are impressive, including a bath house, civilian buildings outside the fort, temples and full size reconstructions of the turf and stone versions of Hadrian’s Wall. Excavations have revealed a succession of forts, the earliest pre-dating construction of the wall, with evidence that the fort was occupied after the end of Roman rule. In some areas soil conditions have allowed the survival of organic objects ranging from items of clothing, shoes and, most famously, a large number of documents (the Vindolanda Tablets) that give a real insight into life on the northern frontier. Much of this is at the excellent museum. In 2006 one of the star finds was an inscription to the previously unrecorded goddess Gallia, the personification of Gaul (modern France), the original home of the unit based at Vindolanda in the third century AD. Look out for the strange and puzzling circular stone huts, thought by some to be part of a prison camp for captured Caledonians.

Carrawburgh (Brocolitia)

The site of the fort at Carrawburgh is marked by an earthwork platform that defines the line of the former defences. But the great attraction here is not the fort, but what lies just south west of it, below the defences. This is a well-preserved temple to the eastern god Mithras. The cult of Mithras was very popular with the army and was probably introduced to Britain by soldiers who had served in the eastern empire. The plan of the temple is similar to that of some early Christian churches – interesting, in view of the fact that the cult of Mithras was, at one point, viewed as a serious rival to the early Christian movement. At one end of the temple are replicas of three altars found on the site (the originals are now in the Museum of Antiquities at Newcastle). Two of these name commanding officers from the fort garrison in the early third century, the First Cohort (regiment) of Batavians who came from what is now the south of Holland, close to the mouth of the Rhine. Close by the temple, a shrine to a local water goddess, Coventina, was discovered in the 19th century, proof of the diversity of Roman religious belief on the frontier.

Chesters (Cilurnum)

The fort at Chesters has probably the most picturesque setting of all the forts. It lies in beautiful parkland next to the River Tyne, and was one of the first to be extensively excavated in the 18th and 19th centuries. Within the fort, barracks, the commanders’ house and the headquarters building (principia) are all visible. The principia has a remarkable and well-preserved sunken strong-room which, when excavated in the late 18th century, still had its wooden door in place. Sadly this disintegrated soon after being exposed to the air.

The highlight, and one of my favourite places on the wall, is the exceptionally well-preserved bath house, with walls up to ten feet high, that lies on the bank of the river. Close by, the massive piers that carried Hadrian’s Wall over the river on a monumental bridge can still be seen and blocks from the bridge litter the river bed. Moving west from Chesters, the country becomes much wilder and more of the wall survives. As a bonus, the fort also has the Clayton Collection of sculpture, inscriptions and other material from many sites along the wall. These include many stones that name the tribes from southern Britain who provided labour for repairs to the wall in the third or
fourth centuries.

Wallsend (Segedunum)

As its modern name implies, this fort was at the eastern end of the wall and a short length can still be seen close to the north bank of the River Tyne. Its layout can clearly be seen although the remains are in a poor condition, having been built over in more recent times, in stark contrast to better preserved sites like Housesteads and Chesters which lie in more remote areas. What Wallsend can offer though is a great museum with a spectacular viewing platform of the whole site together with some full size reconstructions. There’s a military bath house, based on the one at Chesters (you can even sit on a Roman toilet) and a length of the wall as it may have originally appeared. A new discovery is a series of pits on the north side of the wall, pits which would have held sharpened stakes, the Roman equivalent of a barbed wire entanglement. This suggests a real threat of attack and shows that obstacles were needed to slow down any attempt to approach and scale the wall.

This article was first published by HistoryExtra in March 2016, and the highlights were first published in BBC History Magazine in 2006