The historian who has laid down the proposition that religious unity was the cause of the survival of the Eastern Empire when the Western fell,[293] has made the countervailing admission that between Justinian and Heraclius there was an almost universal centrifugal tendency in the Byzantine State, which was finally overcome only by "the inexorable principle of Roman centralisation,"[294] at a time when it was nearly destroyed by its enemies and its own dissentient forces.[295] Province after province had been taken by the Persians in the East; Slavs and Avars were driving back the population from the northern frontiers, even harrying the Peloponnesus; discontent enabled Phocas to dethrone and execute Maurice (602 A.C.); and Phocas in turn was utterly defeated by the Persian foe; when Heraclius appeared, to check the continuity of disaster, and to place the now circumscribed Empire on a footing of possible permanence. But it is important to realise how far the economic and external conditions conduced to his success, such as it was. Hitherto the populace of Constantinople had been supported, like that of imperial Rome, by regular allowances of bread to every householder, provided from the tributary grain supplies of Egypt. The Persian conquest of Egypt in the year 616 stopped that revenue; and the emperor's inability to feed the huge semi-idle populace became a cause of regeneration, inasmuch as the State was forcibly relieved of the burden, and many of the idlers became available for the army about to be led by the emperor against the menacing Persians. He was reduced, however, to the expedient of offering to continue the supply on a payment of three pieces of gold from each claimant, and finally to breaking that contract; whereafter, on his proposing to transfer his capital to Carthage to escape the discontent, the populace and the clergy implored him to remain, and thus enabled him to exact a large loan from the latter,[296] and to dominate the nobility who had hitherto hampered his action. The victories of Heraclius over the Persians, however, only left the eastern and Egyptian provinces to fall under the Arabs; the first financial result of his successes having been to tax to exasperation the recovered lands in order to repay the ecclesiastical loan with usury; and the circumscribed Empire under his successors could not, even if the emperors wished, resume the feeding of the mass of the citizens. Constantinople, though still drawing some tribute from the remaining provinces in Italy, was thus perforce reduced to a safe economic basis, even as the people in general had been coerced into united effort by the imminent danger from Persia.