Christendom was fortunate in Heraclius. Instead of contemplating either despair or surrender, he called upon the Church to summon all Christians to his aid, and by means of the gold and silver plate presented to him as a war loan by the bishops and clergy, and in command of a large army of volunteers, he beat back the Persians from the very gates of his capital. Not content with a policy of defence, he next invaded Asia, and at the battle of Nineveh utterly destroyed the hosts of Chosroes. The fallen King, deposed by his subjects, was forced to take refuge in the mountains, and later was thrown into a dungeon where he died of cold and starvation. Had the reign of Heraclius ended at this date, it would be remembered as a glorious era in the history of Constantinople; but unfortunately for his fame another foe was to make more lasting inroads on his Empire, already weakened by the Persian occupation. When the Emperor (610-41), like Chosroes, received Mahomet’s letter, he is said to have read it with polite interest. It seemed to him that this fanatic Arab, who hated the Jews as much as the Christians did, might turn his successful sword not only against them but against the Persians. In this surmise Heraclius was right, for under Abu Bakr, now Caliph, or ‘successor’, of Mahomet, since the Prophet had left no son, the Moslems invaded Persia. Unfortunately for Heraclius, they were equally bent on an aggressive campaign against the Christian Empire. ‘There is but one God, Allah!’ With this test, by which they could distinguish friend from foe, the Arab hosts burst through the gate of Syria, and at Yermuk encountered the imperial army sent by Heraclius to oppose them. The Greeks fought so stubbornly that at first it seemed that their disciplined valour must win. ‘Is not Paradise before you?... Are not Hell and Satan behind?’ cried the Arab leader to his fanatical hordes, and in response to his words they rallied, broke the opposing lines by the sudden ferocity of their charge, and finally drove the imperial troops in headlong flight. [Sidenote: Mahometan Victories] After the battle of Yermuk Syria fell and Palestine was invaded. In 637 Jerusalem became a Moslem town, with a mosque standing where once had been the famous temple of Solomon. Mahomet had declared Jerusalem a sanctuary only second in glory to Mecca; and his followers with a toleration strange in that age left under Christian guardianship the Tomb of the Holy Sepulchre and other sacred sites.