Resafa, known in Roman times as Sergiopolis and briefly as Anastasiopolis, was a city located in the Roman province of Euphratensis, in modern-day Syria. It is an archaeological site situated south-west of the city of Ar Raqqah and the Euphrates.
The site dates to the 9th century BC, when a military camp was built by the Assyrians. During Roman times it was a desert outpost fortified to defend against the Sassanid Persians, and a station on the Strata Diocletiana. It flourished as its location on the caravan routes linking Aleppo, Dura Europos, and Palmyra was ideal. Resafa had no spring or running water, so it depended on large cisterns to capture the winter and spring rains. North gate of the city of Resafa, site of Hisham’s palace and court.
Resafa was planted right in the path of the Roman–Persian wars, and was therefore a well-defended city that had massive walls that surrounded it without a break. It also had a fortress.
In the 4th century, it became a pilgrimage town for Christians coming to venerate Saint Sergius, a Christian Roman soldier said to have been martyred in Resafa during the Diocletianic Persecution. A church was built to mark his grave, and the city was renamed Sergiopolis. Indeed, it became the “most important pilgrimage center in Byzantine Oriens in [the] proto-Byzantine period”, with a special appeal to the local Arabs, especially the Ghassanids.
In the 8th century, the Umayyad Caliph Hisham ibn Abd al-Malik (r. 724–743) made the city his favoured residence, and built several palaces around it – Wikipedia