Ctesiphon (Greek Κτησιφῶν) was an ancient city in Mesopotamia, founded in ca. the 4th century BC, located on the left bank of the Tigris, opposite of Seleucia. Its ruins are at a site known as Tell ʿUmar, some 35 km (22 mi) south-east of Baghdad. Hellenistic Ctesiphon was conquered by the Parthians and made the capital of the Parthian Empire in the 1st century. In the Sassanid period, Ctesiphon and Seleucia had grown into a single city, sometimes called Seleucia-Ctesiphon, and in Aramaic Mahuza ("the cities", equivalent to Arabic Al-Mada'in المدائن). Seleucia-Ctesiphon served as the Sassanid capital from AD 226. It was intermittently re-conquered by the Roman Empire in 283, and besieged several times in the Byzantine–Sasanian wars. In the late 6th and early 7th centuries, Seleucia-Ctesipho