In 122 AD, the Emperor Hadrian visited Roman Britannia and ordered the construction of a wall to protect the Roman province from the unconquered Celtic tribes to its north. For five years, the governor Aulus Platorius Nepos oversaw its construction. Once completed, Hadrian’s Wall protected Britannia for nearly three centuries, except for a period of twenty-two years when the Romans experimented with the Antonine Wall further north.
When Hadrian assumed power after the death of Trajan, he revised the Empire’s strategic posture to one of defending the lands it already held without resorting to fresh military conquests. His own military and administrative background had already taught him much about defensive structures. Shortly after his accession, northern Britain was the site of a major foreign incursion, and after it was put down, Hadrian decided to improve the province’s defenses, in order to prevent another attack of this nature. The comparatively narrow frontier, relative to those in continental Europe, Asia and Africa, enabled him to plan a much more solid defense than elsewhere.
Based upon his own observations, Hadrian envisioned a solid wall running from the river Tyne to the Solway Firth. By Roman reckoning, this ran 76 miles; in modern terms, it would be about 70 miles. The eastern three-fifths was to be built of stone, with the western two-fifths built instead of earthworks. In either case, the wall was to include a small fort known as a Milecastle every mile along its length. Two smaller towers were built between each Milecastle, and all of these structures were built flush with the wall on their northern side. Each Milecastle incorporated a gate at both ends, permitting soldiers to pass through the wall to fight on the other side when necessary. Just north of the wall was a ditch dug eight or nine feet into the ground, spanning roughly 30 feet. With each slope cut to a 30 degree angle, it was an effective barrier to any fast-moving attack.
Three legions were maintained in Britain at that time: the II Augusta, the VI Victrix pia fidelis, and the XX Valeria Victrix. These were sent north to perform the primary tasks of digging and construction. Remembering the strong engineering component of the Roman legionary system, this was a very sensible choice. It is presumed that locals also participated in the construction in some way, but details are not given. The legions were spread out over the length of the wall, maintaining unit cohesion as the effort progressed.
Primary tasks included the digging of the ditch and of the wall’s foundation, the leveling of the berm between the two, and the construction of the walls and buildings themselves. Secondary tasks included the quarrying of the limestone used in the east, the cutting of turf blocks used in the west, the creation of mortar, and the transportation of all of the building materials, which also included smaller stones for fill within walls and the heavy quantities of water needed for the mortar.
As construction progressed, governor Nepos altered the plan. The pattern of Milecastles and towers was supplemented by the addition of fourteen true forts, replacing every seventh Milecastle. Archaeological work has demonstrated that existing Milecastles and towers were torn down to accommodate the new forts. The walls that were as yet incomplete were finished with a width of only about six feet, instead of the nine originally intended. Secondly, earthen walls flanking another ditch were built parallel to the wall on the southern side; known as the Vallum, this provided yet another barrier to the penetration of the wall, although it is not clear whether it was intended to protect against northern enemies breaking through the wall and moving south, or a possible uprising in the south moving north to attack the soldiers along the wall.
This wall was completed in 127 AD., and it remained Britannia’s northern defense until 142. In that year, the Romans built a new wall much further north. Known as the Antonine Wall, this structure was roughly half the length of Hadrian’s Wall, but in broader strategic terms it was much less successful. Luttwak (pp. 88-89) has argued that it failed because the tribes between the two walls did not sufficiently adapt to the Roman way of life, while the tribes north the Antonine Wall were not sufficiently cowed by Roman power. Already in 158 AD, the repair and expansion of Hadrian’s Wall began, and in 164 it again became the northern boundary of Roman Britannia.
Two notable changes were made at this time. Firstly, the eastern portion was rebuilt in stone, replacing the previous earthwork defenses. Secondly, a road was built parallel to the wall, improving the speed with which decisively large units of soldiers could move to counter any threat along the wall.
The wall was manned by auxiliary troops, while the legions themselves remained concentrated in their respective bases, ready to march to counter any large-scale threat. It was an effective system. From 164 AD to the beginning of the fifth century, it served its function well. In the end, it failed only because it was no longer manned; between 407 and 411, Roman troops were ordered back to the continent to deal with threats there. Without soldiers to defend it, Hadrian’s Wall became merely a physical obstacle to be crossed. For nearly three hundred years, however, it had served to protect Roman Britain.
Fields, Nic. Hadrian’s Wall AD 122-410. Osprey, 2003.
Goldsworthy, Adrian. The Complete Roman Army. Thames & Hudson, 2003.
Luttwak, Edward N. The Grand Strategy of the Roman Empire: From the First Century A.D. to the Third. Johns Hopkins, 1976.
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