While Khaled and one fanatical Saracen horde assaulted the Persian frontier on the lower Euphrates, another, under Abu Obeida, attacked the eastern or desert front of Syria. Bostra, the first city on the edge of the waste, fell by treachery, a small army under the patrician Sergius was defeated, and the governors of Syria and Palestine sent for aid to the emperor. Hardly yet realising the danger of the crisis, Heraclius sent some reinforcements under his brother Theodore to join the local troops. This army checked the Moslems for some months; and it was considered necessary by the caliph to strengthen the Arab host in Syria by sending thither half the force which had invaded the Persian empire, and Khaled, ‘the Sword of God,’ the most terrible and bloodthirsty of all his fanatical chiefs. In July 634, Theodore was badly defeated by the Saracens at Adjnadin near Gabatha, beyond the Jordan. This ill-success roused the emperor: he poured in further reinforcements, and the enemy were attacked in the late summer of 634 by an army of 80,000 men. [Sidenote: Battle of the Yermuk, 634.] The fate of Syria was settled by the battle of the Hieromax (Yermuk), where the troops of the Empire, after a long and bloody fight, in which they at one time forced the Arabs back to the very gates of their camp, were broken by the fanatical rush of an enemy who preferred death to defeat. ‘Paradise is before you,’ cried Abu Obeida to his wavering host, ‘the devil and hell-fire behind;’ and with their last charge the Arabs broke the line of the legions, and rolled the wearied troops in wild disorder back over a line of precipices and ravines, where thousands perished without stroke of sword, by being cast down the lofty rocks. The army of the East was almost exterminated at the Hieromax, and ere another force could be collected Damascus, the greatest city of eastern Syria, was captured by the enemy, who in spite of accepting its surrender massacred a great part of the population (635).