Hadrian spent more time away from Rome than any emperor before or after him. In twenty-one years of rule, from 117 to 138 AD, he made two extended tours of the empire’s provinces, personally inspecting frontiers, reviewing troops, visiting cities, correcting administrative abuses, and leaving behind a physical record of his passage in the form of temples, baths, aqueducts, and the walls and frontier fortifications whose most famous example still bears his name. He was the most traveled of emperors, the most architecturally prolific, and the most systematically interested in the practical realities of governance at the provincial level. He was also the most controversial figure of the Antonine dynasty, for reasons that have as much to do with his personality as with his policies.

The Roman Empire did not end at a wall. The walls — Hadrian’s in Britain, the German and Raetian limes, the Fossatum Africae in North Africa — were not barriers in the way that a modern border fence is a barrier. They were administrative lines, surveillance infrastructure, and military positioning systems that defined the edge of Roman tax collection and legal authority rather than the edge of Roman cultural or economic influence. The distinction matters because the popular image of Rome crouching behind its walls against pressing barbarians misrepresents the actual relationship between Rome and the peoples beyond its frontiers — a relationship that was commercial, diplomatic, and culturally interpenetrative as well as occasionally violent.