The wall that runs across northern England in many ways represented Roman emperor Hadrian’s new ideology. Reigning from AD 117 to 138, Hadrian abandoned continual conquest and expansion in favour of enclosing the Roman empire within clearly marked frontiers. In some provinces the frontier consisted of a road or a river guarded by forts and towers, while in others (including Germany, Africa and Britain) the frontier lines consisted of running barriers.
The British frontier was more elaborate than the others. In its final version it was strongly held by auxiliary soldiers in 17 forts along the line of the wall, with outposts to the north, and forts in the hinterland as well.
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.
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.
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.
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).
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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.