It became a Byzantine possession during the Early Middle Ages and withstood a siege by the Göktürks in 581. Byzantine rule was slight: there was a small imperial garrison more for the town's protection than for its control. It was useful to Byzantium in two ways: it was an observation point to watch the barbarian tribes, and its isolation made it a popular place of exile for those who angered the Roman and later Byzantine governments. Among its more famous "inmates" were Pope Clement I and Pope Martin I, and the deposed Byzantine Emperor Justinian II.