Menas, diverting from conventional Byzantine tactics, decided to face Khalid and destroy the leading elements of the Muslim army before the main body could join them at Hazir, east of Chalcis. This is known as the Battle of Hazir, which even forced Umar to praise Khalid's military genius. Umar is reported to have said: Abu Ubayda soon joined Khalid at the virtually impregnable fort of Chalcis, which surrendered in June 637. With this strategic victory, the territory north of Chalcis lay open to the Muslims. Khalid and Abu Ubayda continued their march northward and laid siege to Aleppo, which was captured after fierce resistance from desperate Byzantine troops in October 637. The next objective was the splendid city of Antioch, the capital of the Asian zone of the Byzantine Empire. Before marching towards Antioch, Khalid and Abu Ubayda 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. Abu Ubayda sent Khalid northwards, while he marched south and captured Lazkia, Jabla, Tartus and the coastal areas west of Anti-Lebanon Mountains. Khalid moved north and raided territory up to the Kızıl River (Kızılırmak) in Anatolia. Emperor Heraclius had already left Antioch for Edessa before the arrival of the Muslims. He arranged for the necessary defenses in Al-Jazira and Armenia and left for his capital Constantinople. On his way to Constantinople he had a narrow escape when Khalid, after the capturing Marash, was heading south towards Munbij. Heraclius hastily took the mountainous path and, passing through the Cilician Gates, is reported to have said: With the devastating defeat at Yarmouk his empire was extremely vulnerable to Muslim invasion. With few military resources left he was no longer in a position to attempt a military come back in Syria. To