Caracalla, the son of Severus, gave back to the Byzantines the right to govern themselves, but the town had received a hard blow, and would have required a long spell of peace to recover its prosperity. Peace however it was not destined to see. All through the middle years of the third century it was vexed by the incursions of the Goths, who harried mercilessly the countries on the Black Sea whose commerce sustained its trade. Under Gallienus in A.D. 263 it was again seized by an usurping emperor, and shared the fate of his adherents. The soldiers of Gallienus sacked Byzantium from cellar to garret, and made such a slaughter of its inhabitants that it is said that the old Megarian race who had so long possessed it were absolutely exterminated. But the irresistible attraction of the site was too great to allow its ruins to remain desolate. Within ten years after its sack by the army of Gallienus, we find Byzantium again a populous town, and its inhabitants are specially praised by the historian Trebellius Pollio for the courage with which they repelled a Gothic raid in the reign of Claudius II. The strong Illyrian emperors, who staved off from the Roman Empire the ruin which appeared about to overwhelm it in the third quarter of the third century, gave Byzantium time and peace to recover its ancient prosperity. It profited especially from the constant neighbourhood of the imperial court, after Diocletian fixed his residence at Nicomedia, only sixty miles away, on the Bithynian side of the Propontis. But the military importance of Byzantium was always interfering with its commercial greatness. After the abdication of Diocletian the empire was for twenty years vexed by constant partitions of territory between the colleagues whom he left behind him. Byzantium after a while found itself the border fortress of Licinius, the emperor who ruled in the Balkan Peninsula, while Maximinus Daza was governing the Asiatic provinces. While Licinius was absent in Italy, Maximinus treacherously attacked his rival’s dominions without declaration of war, and took Byzantium by surprise. But the Illyrian emperor returned in haste, defeated his grasping neighbour not far from the walls of the city, and recovered his great frontier fortress after it had been only a few months out of his hands [A.D. 314]. The town must have suffered severely by changing masters twice in the same year; it does not, however, seem to have been sacked or burnt, as was so often the case with a captured city in those dismal days. But Licinius when he had recovered the place set to work to render it impregnable. Though it was not his capital he made it the chief fortress of his realm, which, since the defeat of Maximinus, embraced the whole eastern half of the Roman world.