Taq Kasra

Taq Kasra تاق کسری‎
Ruins of Ctesiphon (from the United States Library of Congress)
Location	Ctesiphon, Al-Mada'in, Iraq
Coordinates	33°5′37″N 44°34′51″E / 33.09361°N 44.58083°E / 33.09361; 44.58083Coordinates: 33°5′37″N 44°34′51″E / 33.09361°N 44.58083°E / 33.09361; 44.58083
Height	37 m (121 feet)
Built	ca. 3rd-6th century AD
Architectural style(s)	Persian architecture
Location in Ctesiphon, modern Iraq

Tāq Kasrā, also transcribed as Taq-i Kisra, (Persian: طاق کسری‎‎) and Ayvān-e Kasrā (Persian: ایوانِ کسری‎‎); meaning Iwan of Khosrow) are names given to the remains of a ca. 3rd-6th century Sasanian Persian monument, which is sometimes called the Archway of Ctesiphon. It is 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 considered to be a landmark in the history of architecture, and is the largest single-span vault of unreinforced brickwork in the world.

The exact time of construction is not known with certainty. Some historians believe the founder is Shapour I who ruled Persia from 242 to 272 AD and some other believe that construction possibly began during the reign of Anushiruwan the Just (Khosrow I) after a campaign against the Byzantines in 540 AD. The arched iwan hall, open on the facade side, was about 37 meters high 26 meters across and 50 meters long, the largest man-made, free standing vault constructed until modern times.

The arch was part of the imperial palace complex. The throne room—presumably under or behind the arch—was more than 30 m (110 ft) high and covered an area 24 m (80 ft) wide by 48 m (160 ft) long. The top of the arch is about 1 meter thick while the walls at the base are up to 7 meters thick. It is the largest vault ever constructed in the world. The catenary arch was built without centring. In order to make this possible a number of techniques were used. The bricks were laid about 18 degrees from the vertical which allowed them to be partially supported by the rear wall during construction. The quick drying cement used as mortar allowed the fresh bricks to be quickly supported by those that were previously laid.