Among the Arabs themselves, before the time of Mohammed, there had been very little interest in medicine. Gurlt notes that even the physician of the Prophet himself was, according to tradition, a Christian. Mohammed's immediate successors were not interested in education, and their people mainly turned to Christian and Jewish physicians for whatever medical treatment they needed. When the Caliphs came to be rulers of the Mohammedan Empire, they took special pains to encourage the study of philosophy and medicine; though dissection was forbidden by the Koran, most of the other medical sciences, and especially botany and all the therapeutic arts, were seriously cultivated. Until the coming of Mohammed, the Arabs had been wandering tribes, getting some fame as hireling soldiers, but now, under the influence of a feeling of community in religion, and led by the military genius of some of Mohammed's successors, whose soldiers were inspired by the religious feelings of the sect, they made great conquests. The Mohammedan Empire extended from India to Spain within a century after Mohammed's death. Carthage was taken and destroyed, Constantinople was threatened. In 661, scarcely forty years after the _hegira_ or flight of Mohammed, from which good Mohammedans date their era, the capital was transferred from Medina to Damascus, to be transferred from here to Bagdad just about a century later, where it remained until the Mongols made an end of the Abbasside rulers about the middle of the thirteenth century. At the beginning the followers of Mohammed were opposed to knowledge and education of all kinds. Mohammed himself had but little. According to tradition, he could not read or write. The story told with regard to the Caliph Omar and the great library of Alexandria, seems to have a foundation in reality, though such legends usually are not to be taken literally. Certainly it represents the traditional view as to the attitude of the earlier Moslem rulers to education. Omar was asked what should be done with the more than two million volumes. He said that the books in it either agreed with the Koran, or they did not. If they agreed with it they were quite useless. If they did not, they were pernicious. In either case, they should be done away with, because there was an element of danger in them. Accordingly, the precious volumes that had been accumulating for nearly ten centuries, served, it is said, to heat the baths of Alexandria for some six months--probably the most precious fuel ever used. Fortunately for posterity, the edict was not quite as universal in its application as the story would indicate, and exceptions were made for books of science.