Ctesiphon was one of the great cities of ancient Mesopotamia and the capital of the Iranian Parthian Empire and its successor, the Sassanid Persian Empire, for more than 600 years.
Located approximately 20 miles southeast of the modern city of Baghdad, along the river Tigris, it rose to prominence along with the Parthian Empire in the first century BC, and was the seat of government for most of its rulers. Ctesiphon measured 30 square kilometers (cf. the 13,7 square kilometers of imperial Rome).
Because of its importance, Ctesiphon was a major military objective for the leaders of the Roman Empire in its eastern wars. The city was captured by Roman or Byzantine forces five times in its history, three times in the second century alone. The emperor Trajan captured Ctesiphon in 116 and actually annexed it to the Roman Empire, but his successor Hadrian returned it in 117 as part of a peace settlement. The Roman general Avidius Cassius captured Ctesiphon during another Parthian war in 164, but abandoned it when peace was concluded. In 197, the emperor Septimius Severus sacked Ctesiphon and carried off thousands of its inhabitants, possibly as many as 100,000, whom he sold into slavery.
Late in the third century, after the Parthians had been supplanted by the Sassanids, the city again became a souce of conflict with Rome. In 295, Galerius was defeated by the Persians outside the city. Humiliated, he returned a year later and won a tremendous victory which ended in the fourth and final capture of the city by a Roman army. He returned it to the Persian king Narses in exchange for Armenia.
Finally, in 627, the eastern Roman emperor Heraclius took the city, then capital of the Sassanid empire, leaving it after the Persians accepted his peace terms.
Ctesiphon fell to the Islamic Saracens in 637 and went into a rapid decline, especially after the founding of Baghdad not long after.
The ruins of Ctesiphon were the site of a major battle of World War I in November of 1915. The Ottoman Empire defeated troops of Britain attempting to capture Baghdad, and drove them back some 40 miles before trapping the British force and compelling it to surrender.
The splendor of Khosrau's palace at Cetesiphon ( Taq-i Kasra ) is legendry. The Throne room was more than 110 ft high. The massive barrel vault covered an area 80ft wide by 160 ft long.
The arch of Ctesiphon, or Taq-e Kasra, is now all that remains of a city that was, for seven centuries, the main capital of the successor dynasties of the Achaemenids, Parthians and Sasanians. The structure left today was the main portico of the audience hall of the Sasanians who maintained the same site chosen by the Parthians and for the same reason, namely proximity to the Roman Empire whose expansionist aims could be better contained at the point of contact.
Taq-e Kasra (Vault of Khosrow/Khosrau) in the today's Iraqi city of Mada'en, also referred to as Iwan-e Mada'en, near the capital Baghdad is on the verge of collapse. The world-famous monument known as the largest and most unique vault ever constructed in Persia, during the reign of Sassanid dynasty, has been greatly neglected in recent.