Taq Kasra

Taq Kasra (‎‎called Eyvān-e Kasra meaning Iwan of Khosrau), is a Sassanid-era Persian monument located near the modern town of Salman Pak, Iraq. It is the only visible remaining structure of the ancient city of Ctesiphon. The archway is the largest single-span vault of unreinforced brickwork in the world. The Taq Kasra is now all that remains above ground of a city that was, for seven centuries—from the 2nd century BC to the 7th century AD—the main capital of the Iranian successor dynasties of the Parthians and Sassanids.