The siege of Damascus (634) lasted from 21 August to 19 September 634 before the city fell to the Rashidun Caliphate. Damascus was the first major city of the Eastern Roman Empire to fall in the Muslim conquest of Syria. The last of the Roman–Persian Wars ended in 628, after Heraclius concluded a successful campaign against the Persians in Mesopotamia. At the same time, Muhammad united the Arabs under the banner of Islam. After his death in 632, Abu Bakr succeeded him as the first Rashidun Caliph. Suppressing several internal revolts, Abu Bakr sought to expand the empire beyond the confines of the Arabian Peninsula.

In April 634, Abu Bakr 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.