=Battle of Kâdessia, 636 A.C.=—The king of Persia was not willing to let a valuable part of his kingdom go into the hands of the despised Arabs. His pride was broken on the field of Kâdessia. One of the first acts of the new Caliph was to prohibit any expedition beyond the Zagros Mountains, which he considered should always form the boundary between the Caliphate and the Persian dominions; but the subjects of the King of Kings had not laid to heart the lessons of Kâdessia, and harassed the Moslem territories by constant raids. The Caliph was compelled to withdraw his prohibition, and an army marched into Persia. =Battle of Nehâwand, 642 A.C.=—The battle of Nehâwand shattered for ever the empire of the Chosroes. ‘The administration of Persia was regulated by an actual survey of the people, the cattle, and the fruits of the earth; and this monument which attests the vigilance of the Caliphs might have instructed the philosophers of every age.’[37] A similar survey was made, under the Caliph’s orders, of Chaldæa and Mesopotamia; peasants and proprietors alike were guaranteed in the possession of their lands and in the free enjoyment of their religion; the assessment was revised, and a network of canals for the improvement of irrigation was taken in hand. =War with Byzantium.=—In the west the defeat of the Syrians had led Heraclius, the Byzantine Emperor, to send large armies to drive back the Arabs. =Battle of Yermuk, Aug. 634 A.C.—Battle of Ajnâdin, 636 A.C.=—The victories of Yermuk and Ajnâdin put an end to Byzantine rule in Syria. =Capitulation of Jerusalem.=—Jerusalem submitted to the Caliph in person. Travelling with a single attendant, without escort and without any pomp or ceremony, Omar arrived at Jâbia, where he was met by a deputation of Christian notables. To them he accorded the free exercise of their religion, and the possession of their churches, subject to a light tax. Accompanied by the deputation, he proceeded towards Jerusalem, where he was received by Sophronius the Patriarch. The Chief of Islâm and the head of the Christians entered the sacred city together, conversing on its antiquities. The Caliph declined to perform his devotions in the church where he chanced to be at the hour of prayer, ‘for,’ he said to the Patriarch, ‘had I done so, the Mussulmans in a future age might have infringed the treaty under colour of imitating my example.’[38]