The Man from Toronto

In AD 117, Rome ruled more territory than at any point in its history. Its new emperor immediately began giving some of it back. Trajan had spent his final years pushing east. He annexed Armenia, organized a province in Mesopotamia, captured the Parthian capital of Ctesiphon, and reached the Persian Gulf. By most estimates the empire now covered about five million square kilometers. Then the conquered east erupted behind him. Mesopotamian cities revolted, Jewish uprisings tore through Cyrenaica, Egypt, and Cyprus, and Trajan died in Cilicia that August with none of it secured. His successor, Hadrian, had been governor of Syria and inherited the wreckage. He abandoned Mesopotamia and Assyria and returned Armenia to client rule. It was not popular. Early in his reign four ex-consuls tied to Trajan’s regime were executed, and Hadrian spent years insisting the Senate had acted without his orders. But the withdrawal followed the evidence. Trajan’s new provinces had lasted at most three years. Taking Ctesiphon required an army. Holding Mesopotamia would have required one permanently, on the edge of a rival empire, with the interior still burning. Hadrian spent the rest of his reign on control. He was away from Italy for more than half of it, touring the provinces and inspecting the legions. At Lambaesis in North Africa, in 128, he watched the Third Augustan Legion drill and critiqued its performance, and part of his address survives, inscribed on stone. This was an emperor auditing his army. Then he marked the limits. In Britain he built a wall of roughly 80 miles, which his biographer says was meant to separate Romans from barbarians. In Germany he raised a timber palisade. But these were not walls in the modern sense. Hadrian’s Wall had a gate at every milecastle, so it worked as a checkpoint, regulating movement rather than simply denying it. It would be wrong to call this pacifism. Tacitus says Augustus had already advised keeping the empire within its limits, and Rome never stopped being able to expand. Hadrian crushed the Bar Kokhba revolt in Judaea in a war of that was incredibly brutal. His successors reached east again. Lucius Verus sacked Ctesiphon in 165. Marcus Aurelius is reported to have considered new provinces north of the Danube. Septimius Severus eventually established a Roman province of Mesopotamia in 198. The capacity for conquest remained. Hadrian changed which question came first. Rome had spent centuries asking how much more it could conquer. Hadrian asked whether more conquest would actually make Rome stronger. His answer was not retreat, but triage. Hold what can be held, fortify what must be fortified, and match the empire’s size to its capacity to govern. Rome had reached its greatest extent under Trajan. Under Hadrian, it began learning how to live within its limits.