After a siege lasting almost a month the Rashidun Arabs under Khalid ibn al-Walid capture Damascus from the Byzantine Empire (Eastern Roman Empire).
The Siege of Damascus lasted from 21 August to 19 September 634 AD before the city fell to the Rashidun Caliphate. Damascus was the first major city of the Byzantine (Roman) empire to fall in the Muslim conquest of Syria.
In April 634, Abu Bakr (the first Rashidun Caliph) invaded the Byzantine Empire in the Levant and decisively defeated a Byzantine army at the Battle of Ajnadayn. The Muslim armies marched north and laid siege to Damascus. The city was taken after a monophysite bishop informed Khalid ibn al-Walid, the Muslim commander in chief, that it was possible to breach city walls by attacking a position only lightly defended at night. While Khalid entered the city by assault from the Eastern gate, Thomas, commander of the Byzantine garrison, negotiated a peaceful surrender at the Jabiyah gate with Abu Ubaidah, Khalid’s second in command.
After the surrender of the city, the commanders disputed the terms of the peace agreement. The commanders finally agreed that the peace terms given by Abu Ubaidah would be met. The peace terms included an assurance that no pursuit will be undertaken by Muslims against the departing Roman convoy for three days. Having acquiesced to the peace terms, it was three days after the surrender of the city that Khalid set out after the Damascan refugees towards Antioch and defeated them in battle six days later, near present day Al Jayyad.