Around AD 260 the Roman emperor Valerian entered upon his new, brief, and ignominious career as the mounting block of Shapur I, one of the most dynamic kings of Persia. Shapur had laid siege to the eastern cities of Carrhae and Edessa in a bid to recover those ancient territories of Achaemenid Persia then under Roman control. Valerian marched out at the head of the Roman army and was defeated and captured. The Christian author Lactantius, ecstatic at the fall of a persecutor of the faith, supplies the humiliating story that whenever he wished to mount his horse Shapur ordered Valerian to bend over and present his back. Placing his foot on Valerian’s shoulder, the king remarked on the true power relations between the empires, as opposed to the fictions of Roman propaganda. Shapur himself memorialised his triumph dramatically by carving reliefs of a bound Valerian into the cliffs of his Persian homeland. Roman generals and emperors had been killed in battle before, but Valerian was the first emperor to be taken prisoner in war.

Valerian’s disgrace is just one symbol of the crisis that gripped the Roman empire in the second half of the third century AD. Wars in the