Before marching towards Antioch, Khalid and Abu Ubaidah decided to isolate the city from Anatolia. Accordingly, they sent detachments north to eliminate all possible Byzantine forces and captured a garrison town, Azaz from Aleppo; from there the Muslims attacked Antioch on the eastern side. In order to save the empire from annihilation, a desperate battle was fought between the Muslim army and that of the defenders of Antioch, popularly known as Battle of Iron Bridge. The Byzantine army was composed of the survivors of Yarmouk and other Syrian campaigns. After being defeated, the Byzantines retreated to Antioch and the Muslims besieged the city. Having little hope of help from Emperor Herakleios, Antioch surrendered on 30 October 637, with the terms that all Byzantine troops would be given safe passage to Constantinople.