The second phase began with the arrival of Khalid ibn al-Walid and his troops to Syria in 634. Under Khalid's supreme command, the Muslim armies besieged and captured the southern Syrian urban centers of Bosra, Damascus, Beisan (Scythopolis), Pella, Gaza, and temporarily, Homs (Emesa) and Baalbek (Hierapolis). Heraclius responded by deploying successive imperial armies against the Muslims. The Byzantines were decisively defeated in the resulting major battles of Ajnadayn in Palestine and Fahl and Yarmouk in Transjordan, all occurring in 634–636. The Muslim battlefield victories effectively ended organized resistance by the Byzantines.