A further stimulus would come from the overthrow of the Parthian empire of the Arsacidæ by Artaxerxes, 226 A.C. The Arsacidæ, though often at war with the Romans, still represented the Hellenistic civilisation, whereas the Sassanidæ zealously returned to the ancient Persian religion, the exclusiveness of which would serve as a barrier to Western commerce,[285] even while the cult of Mithra, Hellenised to the extent of being specially associated with image-worship, was spreading widely in the West. Commerce would now tend afresh to concentrate in Greece, the Indian and Chinese trade passing north and south of Persia.[286] The removal of the seat of government from Rome by Diocletian, greatly lessening the Italian drain on the provinces, would still further assist the Greek revival after the Gothic invasion had come and gone. Thus we find the larger Greek world in the time of Constantine grown once more so important that in the struggle between him and Licinius his great naval armament, composed chiefly of European Greeks, was massed in the restored Piræus. The fleet of Licinius, made up chiefly by Asiatic and Egyptian Greeks, already showed a relative decline on that side of the Empire's resources.[287] When, finally, Constantine established the new seat of empire at Byzantium, he tended to draw thither all the streams of Greek commerce, and to establish there, as the centre of the revenues of the Eastern Empire, some such population as had once flourished in Rome; with, however, a definite tendency to commerce and industry in the lower class population as well as in the middle class. To the government of this population was brought the highly developed organisation of the later Pagan Empire, joined with an ecclesiastical system from which heresy was periodically eliminated by the imperial policy, aided by the positive intellectual inferiority of the new Greek-speaking species. There was prosperity enough for material life; and the political and religious system was such as to prevent the normal result of prosperity, culture, from developing independently. The much-divided Greek world had at last, after countless convulsions, been brought to a possibility of quasi-inert equilibrium, an equilibrium which enabled it to sustain and repel repeated and destructive irruptions of northern barbarism,[288] and on the whole to hold at bay, with a shrunken territory, its neighbouring enemies for a thousand years. § 4