Hadrian's Wall was built following a visit by Roman emperor Hadrian (AD 76–138) in AD 122. Hadrian was experiencing military difficulties not just in Britain, but from the peoples of various conquered lands across the Empire, including Egypt, Judea, Libya, Mauretania, and many of the peoples conquered by his predecessor Trajan, so he was keen to impose order. However the construction of such an impressive wall was probably also a symbol of Roman power, both in occupied Britain and in Rome.
Hadrian's Wall was 80 Roman miles (73.5 Imperial miles or 120 kilometres) long, its width and height dependent upon the construction materials which were readily available nearby to build it from: east of the river Irthing the wall was made from stone and measured 10 Roman feet (9.7 ft or 3 m) wide and 5 to 6 metres (16–20 ft) tall; west of the Irthing the wall was made from turf and measured 6 metres (20 ft) wide and 3.5 metres (11.5 ft) high. This does not include the wall's ditches, berms, and forts. The central section measured 8 Roman feet wide (7.8 ft or 2.4 m) on a 10 foot base.
Hadrian's Wall extended due west from Wallsend on the River Tyne to the shore of the Solway Firth. The A69 and B6318 roads largely follow the course of the wall as it starts in Newcastle upon Tyne to Carlisle, then on round the northern coast of Cumbria. The Wall is entirely in England and south of the border with Scotland by 15 kilometres (9 mi) in the west and 110 kilometres (68 mi) in the east.
The wall was garrisoned by auxiliary (i.e., non-legionary) units of the army (non-citizens). Their numbers fluctuated throughout the occupation, but may have been around 9,000 strong in general, including infantry and cavalry. The new forts could hold garrisons of 500 men whilst cavalry units of 1,000 troops were stationed at either end. The total number of soldiers manning the early wall was probably greater than 10,000.
They suffered serious attacks in 180, and especially between 196 and 197 when the garrison had been seriously weakened, following which major reconstruction had to be carried out under Septimius Severus. After the harsh suppression of the tribes under Septimius, the region near the wall remained peaceful for most of the rest of the 3rd century. It is thought that many in the garrison may have married and integrated into the local community.
In the months after Hadrian's death in 138, the new emperor, Antoninus Pius essentially abandoned the wall, though leaving it occupied in a support role, and began building a new wall in Scotland proper, about 160 kilometres (100 mi) north, the Antonine Wall. This turf wall ran 40 Roman miles (about 37.8 mi or 61 km) and had significantly more forts than Hadrian's Wall. Antonine was unable to conquer the northern tribes and so when Marcus Aurelius became emperor, he abandoned the Antonine Wall and occupied Hadrian's Wall once again in 164. It remained occupied by Roman troops until their withdrawal from Britain.
In the late 4th century, barbarian invasions, economic decline, and military coups loosened the Empire's hold on Britain. By 410, the Roman administration and its legions were gone, and Britain was left to look to its own defences and government. The garrisons, by now probably made up mostly of local Britons who had nowhere else to go, probably lingered on in some form for generations. Archaeology is beginning to reveal that some parts of the Wall remained occupied well into the 5th century. But in time the wall was abandoned and fell into ruin. Over the centuries a large proportion of the stone was reused in other local buildings. This continued until the 20th century.