Nevertheless there is much that remains enigmatical in the immense success that attended the Moslems. Their armies were not very large. The emperor Heraclius was an able man, with all the prestige of victory behind him. When the great struggle of Moslem and Persian began, the civil wars of the empire were over, and it had a powerful leader--not indeed in Yezdegerd, its youthful monarch, but in the mighty prince Rustem, who had procured the crown for him. The great financial straits to which both empires were unquestionably reduced must have had its effect upon the number and efficiency of their troops, but that they were still good for something is clear from the fact that both the decisive battle on the river Yarmuk (August, 636) in which the Romans were defeated, and that of Kadisiya (end of 636 or beginning of 637) in which a like fate waited on the Persian arms, lasted for several days. The resistance offered must have been very obstinate. The Roman and Persian armies may have included irregular troops of various kinds, but they certainly consisted largely of disciplined soldiers under experienced officers. The Persians brought elephants into the field, as well as their dreaded mounted cuirassiers. Among the Arabs there was no purely military order of battle; they fought in the order of their clans and tribes. This, though it probably insured a strong feeling of comradeship, was by no means an adequate equivalent for regular military units. Freiherr von Kremer[20] rightly sees in the salat a substitute, to some extent, for military drill. In that ceremony the Arabs, hitherto wholly unaccustomed to discipline, were obliged _en masse_ to repeat the formulæ with strict exactitude after their leader and to copy every one of his movements, and any man who was unable to perform the salat with the congregation was none the less bound to strict compliance with the form of prayer in which he had been instructed. But the main factor was the powerful corporate feeling of the Moslem, the ever increasing enthusiasm for the faith even in those who had at first been indifferent, and the firm conviction that the warriors for the holy cause, though death in the field would prevent them from taking a share in the spoils of victory on earth, would yet partake of the most delightful of terrestrial joys in heaven. Thus the masterless Arabs, who, for all their turn for boasting, had but little stomach for heroic deeds, were transformed into the irresistible warriors of Allah. It was the highest triumph of Semitic religious zeal, a manifestation on a vast scale that among the Arabs the sense of religion had only slumbered, to awaken when occasion arose with true Semitic fury. The same thing has since come to pass again and again on a smaller scale.