What is peculiar to the Saracen civilisation is its sudden origin (taking Islam as a history by itself)[381] under conditions reached elsewhere only as climax in a long evolution. The rise of Islam has the twofold aspect of a barbarian campaign of plunder and a crusade of fanaticism; and though the prospect and the getting of plunder were needed to ripen the fanaticism to full bloom,[382] the latter was ultimately a part of the cementing force that turned a horde into a community. The great facilitating conditions for both were the feeble centralised system maintained by the Christianised Empire, and the disintegrating force of Christianity as a sectarian ferment. In Egypt, for instance, the hatred between rival schools of Christian metaphysic secured for the Arabs an unresisted entrance into Alexandria.[383] It needed only a few generations of contact with higher culture in a richer environment to put the Saracens, as regards art and science, very much on a level with the stagnating Byzantines; and where the latter, possessed of their scientific and philosophical classics, but imprisoned by their religion, made no intellectual progress whatever, the former, on the same stimulus, progressed to a remarkable degree. There has been much dispute as to the exact measure of their achievements; but three things are clear: (1) that they carried the mathematics of astronomy beyond the point at which it had been left by the Greeks; (2) that they laid the foundations of chemistry; and(3) that they intelligently carried on surgery and medicine when the Byzantines, having early in the Christian period destroyed the Asklepions, which were in some degree the schools of the medicine of antiquity, had sunk to the level of using prayers and incantations and relics as their regular means of cure. Curiously enough, too, the Saracens had the merit, claimed for the Byzantines, of letting their women share rather freely in their culture of all kinds.[384] What is more, the later Saracens of Spain, whatever the measure of their own scientific progress, were without question a great seminal force in the civilisation of Western Christendom, which drew from them its beginnings in mathematics, philosophy, chemistry, astronomy, and medicine, and to some extent even in literature[385] and architecture,[386] to say nothing of the effect on the useful arts of the contact of the Crusaders with the Saracens of the East.