Abu Ubaida ibn al-Jarrah, the supreme commander of the Muslim armies in Syria, had ordered Shurhabil ibn Hasana to attack Bosra. The latter laid siege to Bosra with his small army of 4000. The Roman and Ghassanid Arab garrison, realizing that this might be the advance guard of the larger Muslim army to come, sallied out of the fortified city and attacked Shurhabil, surrounding him from all sides; however, Khalid reached the arena with his cavalry and saved Shurhabil. The combined forces of Khalid, Shurhabil, and Abu Ubaidah then resumed the siege of Bosra, which surrendered some time in mid-July 634 CE, effectively ending the Ghassanid Dynasty. Here Khalid took over the command of the Muslim armies in Syria from Abu Ubaidah, according to the instructions of the Caliph.