The ancient city of Ctesiphon was located on the eastern bank of River Tigris, approximately 32 km southeast of modern Bagdad in Iraq. It is said that, when Seleucus established the Hellenistic city of Seleucia in 312 BC on the west bank of the Tigris, the Greek army camped on the opposite side of the river, known as Ctesiphon. The city of Ctesiphon was founded probably in the late 120s BC, on the site of that military camp. It remained just like that until the 2nd century BC, when the Parthians seize a part of Mesopotamia. They developed a new town on the site of Ctesiphon, which soon formed a famous twin city, with the older Seleucia on the other bank of the river. With time, the course of the river changed its direction and started to flow between the ruins of the two cities. In fact, it divided the city of Ctesiphon into two.
During the 2nd century AD the twin city changed hands several times between Romans and Parthians. Vardanes I, who was a Parthian prince of Iranian and Greek ancestry, forced the city of Seleucia in 43 AD, to submit to the Parthians after a rebellion of seven years. Consequently, Vardanes I was hailed by a portion of the people, who were gained by this war and they named him as the founder of Ctesiphon.
Seleucia was largely destroyed by the Romans in 165. The city of Ctesiphon was captured by Rome five times in its history and three times in the 2nd century alone. But, it flourished fluently during the days of the Sasanian Dynasty. Ardashir, the founder of the Sasanian dynasty, entered Ctesiphon in triumph in AD 224. The city's most famous building, the great vaulted Taq-i Kasra, sometimes called the Archway of Ctesiphon, was built in the same dynasty. It is believed to have been built in the 6th century by Khosrau I, as his palace, adorned with a large vaulted arch.
The Taq-i Kasra, is the only remaining structure of the ancient city of Ctesiphon. The enormous archway had only one opening on the façade side. Its arched rectangular vaulted hall was about 37 metres high, 26 metres across and 50 metres long. The gigantic structure, the largest single-span vault of brickwork in the world, is still considered as a wonderful landmark in the history of architecture. It was a part of the Imperial Palace complex and the throne room behind it was said to be about 110 feet high, 80 feet wide and 160 feet long.
The Byzantine Emperor Heraclius surrounded the capital city of the Sasanian Empire in 627, but he left it after the Persians accepted his peace terms. However, a deadly plague hit Ctesiphon, along with the rest of the western part of the Sasanian Empire in 628, which even took the life of Kavadh II, son and successor of Khosrau.
The Arabs conquered the city in 637 AD and transformed the Ṭāq-i Kasrā into an improvised mosque and as the newly founded city of Bagdad started to flourish, Ctesiphon lost its past glory and was gradually abandoned. The deserted ruins of the city, along with the remains of Taq-i Kasra were plundered and were used as a quarry for building materials. The final blow came in 1888, when one third of the spectacular structure was swept away by a flood.
In1928–29 and 1931–32, University of Pennsylvania and a German Oriental Society excavated mainly on the western part of Ctesiphon. An Italian team from the University of Turin also worked to restore the palace of Khosrau II, in the late 1960s and early 1970s. The former museum was shamelessly looted and vandalized after the fall of Saddam Hussein. Unfortunately, Taq-i Kasra, the largest brick-built arch in the world and a sad reminder of one of the greatest cities of ancient Mesopotamia, is now counting its days and surviving with the apprehension of being destroyed by the harsh weather and the threat from the Islamic State.