Though its exact location is not known, it was located on the major route to Khorasan, between Seleucia and the Zagros Mountains. According to Isidore of Charax, it was crossed by the river Sillas (Diyala) and was located about 82 km from Seleucia, and was also known as Chalasar. It was originally a Greek (Macedonian) foundation, but was later considered Parthian. In AD 31, It welcomed the Arsacid pretender Tiridates II.