The reign of Justinian (527--65) was a key phase in the transition from the Roman empire of classical times to the Byzantine empire of the Middle Ages. Justinian himself, born of peasant stock in a provincial backwater, was one of the greatest rulers yet, despite prodigious achievements, he remained an outsider in the sophisticated society of Constantinople. Here, John Moorhead reinterprets Justinian as man and monarch, together with his formidable empress, the ex-actress Theodora, and assesses the evidence from their time for the evolution of a distinctively medieval world.