Ancient city, central Mesopotamia. Located on the Tigris River, southeast of modern Baghdad, Iraq, it was first a Greek army camp opposite the Hellenistic city of Seleucia. It was the capital of Parthia in the 2nd century BC. Destroyed by the Romans in AD 165, it was resettled by the Persian Sasanian dynasty in the 3rd century. The Arabs conquered the city in 637 but abandoned it by 763 in favour of a new city, Baghdad. The site is famous for the remains of a gigantic vaulted hall, the Taq Kisra, which has one of the largest single-span brick arches in the world.