Ctesiphon

The ancient city of Ctesiphon, on the banks of Tigris, is located about 35 km southeast of modern Baghdad. Established in the late 120s BC, it was one of the great cities of late ancient Mesopotamia and the largest city in the world from 570 AD, until its fall in 637 AD, during the Muslim conquest.

The only surviving structure of Ctesiphon today is the majestic, vaulted hall of Taq Kasra. The archway is one of the largest single-span vault of unreinforced brickwork in the world consisting of two main parts: the building itself and the arch next to it. The arch is 37 meters high, 26 meters wide and 50 meters high. The top of the arch is about 1 meter thick while the walls at the base are up to 7 meters thick and is considered one of the greatest buildings of its kind of time. The throne room – which is expected to be  behind the arch – was more than 30 meters high, 24 meters wide and 84 meters long.

So what?

Perhaps not many know that this monument represents the largest roofed hall in the world built of proud clay and materials used in its construction  executed in the form of an arch without the use of supports, and there is no other hall built in this wide space (26 meters). This represents an engineering miracle 15 centuries ago because the proud clay does not withstand the forces of tension or bending, which is usually the case with the structural parenting.

The curve name of the arch is catenary shape forms naturally when you suspend a rope or chain from two points. (The word  “catenary” comes from the Latincatena , meaning “chain.”) .

A catenary arch is a type of architectural arch that follows an inverted catenary curve.

Catenary arches are especially strong because they redirect the vertical force of gravity into compression forces that press along the curve of the arch

After the Arabs captured Ctesiphon in 637 AD, they improvised the palace as a mosque until the area was gradually abandoned. By the 8th century, Ctesiphon had been superseded by the newly founded city of Baghdad, and Ctesiphon’s deserted ruins were used as a quarry for building materials. Subsequent floods destroyed all remaining structures, including Taq Kasra, one third of which was swept away by a flood in 1888.The imposing brick ruin of Taq Kasra is now all that remains above ground .

In other words, the arch, which has a height of 37 meters and a width of 26 meters, if carried out by any other dimensions the arch dimension will, generates forces of tension, shear, torque causing the  collapse of the building, and I do not think that this was a coincidence but indicates knowledge and experience of Iraqis at that time.