Ctesiphon became the main royal residence of the Parthian Empire under Mithridates I.
Ctesiphon stood on the eastern bank of the Tigris, opposite Seleucia, in the region of ancient Babylonia. Mithridates I conquered Mesopotamia in the second century BCE, bringing the area and its established urban centers under Parthian control. Ctesiphon then developed into a major royal residence and political center.
The city’s importance continued under the Sasanians, who made it their principal imperial capital. Its famous surviving monument, the Taq Kasra or Arch of Ctesiphon, belongs to the Sasanian period rather than to the earliest Parthian occupation. This difference causes frequent confusion when the city’s long history is summarized.
Ctesiphon’s position near the Tigris helped connect Iranian political power with the wealthy agricultural and urban regions of Mesopotamia. It remained strategically important until the Arab conquest in the seventh century CE.