Resumen
Ctesiphon developed on the east bank of the Tigris opposite Hellenistic Seleucia, consolidating into the twin cities later called al-Mada’in. Parthian kings wintered here; Sasanian shahanshahs made it the ceremonial and administrative heart of Erānshahr from Ardashir I through Khosrow II. Arab armies captured the city in 637 CE after the Battle of al-Qādisiyyah; much of the palace quarter decayed as Baghdad rose.
What remains most dramatically visible is Taq Kasra (the Arch of Khosrow / ayvān of al-Madāʾin): a free-standing baked-brick vault roughly 30 metres high spanning about 25 metres — one of the largest unreinforced brick arches ever built. Excavations and early travellers documented palace complexes, residential mounds, and canalised floodplains; modern damage, flood, and conflict have thinned standing fabric beyond the arch.
The site anchors debates on Sasanian court culture, silk-road diplomacy with Byzantium, and the transfer of imperial capitalship from Mesopotamian to Islamic Iraq. Pair with Hatra and Persepolis for complementary Iranian imperial landscapes, and with Palmyra for late antique caravan politics.