Resafa

Resafa, also sometimes spelled Rusafa, and known in the Byzantine era 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 southwest of the city of Raqqa and the Euphrates.

Procopius describes at length the ramparts and buildings erected there by Justinian. The walls of Resafa, which are still well preserved, are over 1600 feet in length and about 1000 feet in width; round or square towers were erected about every hundred feet; there are also ruins of a church with three apses.

Source: Wikipedia