The politics of Arabia had up to this time been of little moment either to Roman or Persian. Each of them had allies among the Arab tribes, and had sometimes sent an expedition or an embassy southward, into the land beyond the Syrian desert. But neither of them dreamed that the scattered and disunited tribes of Arabia would ever combine or become a serious danger. But while Heraclius and Chosroës were harrying each other’s realms events of world-wide importance had been taking place in the Arabian peninsula. For the first and last time in history there had arisen among the Arabs one of those world-compelling minds that are destined to turn aside the current of events into new channels, and change the face of whole continents. Mahomet, that strangest of moral enigmas, prophet and seer, fanatic and impostor, was developing his career all through the years of the Persian war. By an extraordinary mixture of genuine enthusiasm and vulgar cunning, of self-deception and deliberate imposture, of benevolence and cruelty, of austerity and licence, he had worked himself and his creed to the front. The turbulent polytheists of Arabia had by him been converted into a compact band of fanatics, burning to carry all over the world by the force of their swords their new war-cry, that “God was God, and Mahomet His prophet.” In 628, the last year of the great war, the Arab sent his summons to Heraclius and Chosroës, bidding them embrace Islam. The Persian replied with the threat that he would put the Prophet in chains when he had leisure. The Roman made no direct reply, but sent Mahomet some small presents, neglecting the theological bent of his message, and only thinking of enlisting a possible political ally. Both answers were regarded as equally unsatisfactory by the Prophet, and he doomed the two empires to a similar destruction. Next year [629] the first collision between the East-Romans and the Arabs took place, a band of Moslems having pushed a raid up to Muta, near the Dead Sea. But it was not till three years later, when Mahomet himself was already dead, that the storm fell on the Roman Empire. In obedience to the injunctions of his deceased master, the Caliph Abu Bekr prepared two armies, and launched the one against Palestine and the other against Persia.