2. Why was Hadrian’s Wall built?

The answer to this question was conveniently supplied in Hadrian’s biography, where it was said the emperor ‘was the first to construct a wall, eighty miles in length, which was to separate the barbarians from the Romans’ (Historia Augusta, Life of Hadrian 11). Scholars have suggested many additional reasons (such as the wish of Hadrian to leave a monumental frontier behind him, the need for a project to keep the army occupied, problems with endemic warfare) but these are speculative and this is the only clear statement surviving.

Further reading: Breeze and Dobson 2000