Hadrian's Wall: A Roman frontier crossed northern Britain from sea to sea

Hadrian’s Wall crossed northern Britain between the Tyne and the Solway. Built from the second century AD, the frontier combined walls, ditches, forts, and smaller military posts. Its garrison included auxiliary troops from across the Roman Empire, and its exact purposes extended beyond stopping a single invading army.

Purpose

Hadrian's Wall was probably planned before Hadrian's visit to Britain in 122. According to restored sandstone fragments found in Jarrow which date from 118 or 119, it was Hadrian's wish to keep "intact the empire", which had been imposed on him via "divine instruction". On Hadrian's accession to the imperial throne in 117, there was unrest and rebellion in Roman Britain and from the peoples of various conquered lands across the empire, including Egypt, Judea, Libya and Mauretania. These troubles may have influenced his plan to construct the wall, as well as his construction of frontier boundaries now known as limes in other areas of the empire, such as the Limes Germanicus in modern-day Germany.

The novelty of the wall as a departure from traditional Roman military architecture as typified by the Roman limes has been seen as noteworthy and has led to exceptional suggestions of influence by some scholars; for example, David Breeze and B. Dobson suggest "Hadrian may have been influenced by travellers' accounts of the Great Wall of China, built some two hundred years before." This proposal has been challenged by other scholars like Duncan B. Campbell who argues that, though the scale and design of the wall was novel for Roman military construction, "there was a long tradition of wall-building in the ancient (Mediterranean) world upon which he could have drawn for inspiration without the inconvenience of traversing whole continents in search of a prototype."

Construction

Hadrian ended his predecessor Trajan's policy of expanding the empire and instead focused on defending the current borders, namely at the time Britain. Like Augustus, Hadrian believed in exploiting natural boundaries such as rivers for the borders of the empire, for example the Euphrates, Rhine and Danube. Britain, however, did not have any natural boundaries that could serve the purpose of dividing the province controlled by the Romans from the Celtic tribes in the north.

With construction starting in 122, the entire length of the wall was built with an alternating series of forts, each housing 600 men, and manned milecastles, operated by "between 12 and 20 men". It took six years to build most of Hadrian's Wall with the work coming from three Roman legions – the Legio II Augusta, Legio VI Victrix, and Legio XX Valeria Victrix, totalling 15,000 soldiers, plus some members of the Roman fleet. The building of the wall was not out of the area of expertise for the soldiers; some would have trained to be surveyors, engineers, masons, and carpenters.

Garrison

It is thought that following construction and when fully manned, almost 10,000 soldiers were stationed on Hadrian's Wall, made up not of the legions who built it but by regiments of auxiliary infantry and cavalry drawn from the provinces. Following from this lays out the two basic functions for soldiers on or around Hadrian's Wall. Breeze says that soldiers who were stationed in the forts around the wall had the primary duty of defence; at the same time, the troops in the milecastles and turrets had the responsibility of frontier control. Evidence, as Breeze says, for soldiers stationed in forts is far more pronounced than the ones in the milecastles and turrets.

Breeze discusses three theories about the soldiers on Hadrian's Wall. Firstly, these soldiers who manned the milecastles and turrets on the wall came from the forts near it. Secondly, regiments from auxiliaries were specifically chosen for this role. Thirdly, "a special force" was formed to man these stations. Breeze comes to the conclusion that through all the inscriptions gathered there were soldiers from three, or even four, auxiliary units at milecastles on the wall. These units were "cohors I Batavorum, cohors I Vardullorum, an un-numbered Pannonian cohort, and a duplicarius from Upper Germany". Breeze adds that there appears to have been some legionaries as well at these milecastles.