Parthian and Sasanian kings ruled from a Tigris mega-city
Ctesiphon stood on the Tigris’s east bank about thirty-five kilometres southeast of Baghdad. Merging with Seleucia and neighbours as “the Cities” (Mahoza/al-Mada'in), it grew into a commercial giant that Romans took three times in Parthian wars and again under the Sasanians.
Ctesiphon was founded in the late 120s BC on the site of a military camp that Mithridates I of Parthia had set up opposite Seleucia. It flourished as a political and commercial centre under Gotarzes I and became the capital around 58 BC under Orodes II, perhaps partly because the earlier capitals, Mithradatkirt and Hecatompylos, lay too close to Scythian raids. Gradually it grew together with Seleucia, the former Hellenistic capital, and neighbouring settlements into one cosmopolitan metropolis.
At about 30 square kilometres, it covered more than twice the area of fourth-century imperial Rome, which measured 13.7. The Taq Kasra, a surviving part of the royal palace built sometime between the third and sixth centuries AD, stands in the modern Iraqi town of Salman Pak. Romans captured the city three times during their Parthian wars and fought the Sasanians there in 363, and after the Muslim conquest it declined until it was deserted by the end of the eighth century.
The name has many forms. Greek Ktēsiphôn probably adapts a local name like Tisfōn, written Tyspwn in Middle Persian. Church of the East synods wrote Qṭēspōn, or Māḥôzē for the twin metropolis of Seleucia-Ctesiphon, and Armenians said Tizbon.
Modern Arabic uses Ṭaysafūn, Qaṭaysfūn or al-Mada’in, the Cities, for the greater urban area; the geographer Yāqūt, citing Ḥamza, gave the original as Ṭūsfūn. The Book of Ezra may mention it as Kasfia, related to the ethnic name behind Caspian and Qazvin, and the Talmud calls it Aktisfon, across the Tigris from the city of Ardashir.
Source: Ctesiphon
