The forces now marched upon Damascus, when a change took place in the relative position of the generals. Abu Bekr shortly before his decease, which happened in 634 A.D., had appointed Omar ibn el Khattób his suc cessor. The first act of the new caliph on assuming the reins of government was to depose KMlid from the command of the army in Syria, and to appoint Abu Obeidah generalissimo in his stead. 'Omar's letter con taining these commands reached them outside Damascus, and Abu Obeidah, immediately upon receiving it, posted himself with his division at the Bâb el Jâbieh ; Khàlid occupied the eastern gate, and the two remaining chiefs Yezid ibn Abi Sufiyân, and 'Amer ibn el 'As, having dis posed their forces on the north and south sides respectively, a strict blockade was commenced. For seventy days Damascus held out; when KMlid having forced his position, the inhabitants retreated to the opposite side of the city, and, finding further resistance, impossible, admitted Abu Obeidah peaceably within the walls ; the two generals thus met in the centre of the city. The conquest of Damascus was followed by the taking of Homs, after a protracted siege ; Hamath and Ma'arrah surrendered without a blow; Laodicea, Jebeleh, Tarsus, Aleppo, Antioch, Caesarea, Sebastiyeh, Nablus, Lydda, and Jaffah, one after another fell into the hands of the invaders. But it was at the battle of Yarmuk (A.D. 630) that the Christian power in Syria experienced the most fatal blow. The Emperor Heraclius, driven to desperation by the continued successes of the enemy, had determined upon making a great and final effort for the preservation of his empire in the East. He had accordingly raised an immense army from all parts of his dominions, and despatched the main body to give battle to the Saracens ; while the remaining portion, which was still very considerable in point of numbers, received instructions to defend the seaboard of Syria. On the approach of the Greek army the Arab generals,