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.