18. The Gathering of Armies For the Middle East’s Most Decisive Showdown
In 634, the Arabs simultaneously attacked the Persians in Iraq, and the Byzantines in Syria. However, the forces attacking Syria proved too small for the task, so reinforcements were diverted from the Persian front, where things were going more smoothly. They were led by the Arabs’ greatest general, Khalid ibn al Walid, who assumed command in Syria. In July of 634, Khalid routed the Byzantines at the Battle of Ajnadayn and seized Damascus. He won another victory soon thereafter at the Battle of Fahl, and seized Palestine.
The Byzantines set out to recover their lost territories, and assembled an army of 80,000 to 150,000 men according to modern estimates, that significantly outnumbered their 25,000 to 40,000 Muslim opponents. The Byzantine marched in five grand divisions to the Yarmouk, where they met an Arab army broken into 36 infantry and 4 cavalry regiments, with an elite cavalry force held back as a mobile reserve. Khalid assembled his army along a 7.5-mile front facing west, with his left flank anchored on the Yarmouk river, and his right on heights to the north.