The Ctesiphon arch is considered as one of the many architectural wonders of Mesopotamia. This arch was built in 400 A.D. by the Parthian Persians to be the largest single-span vault of un-reinforced brickwork in the world. The arch has a span of seventy-five feet and is about 110 feet high.It stands in the ancient city of Ctesiphon. Ctesiphon is a historically significant city that lies on the east bank of the Tigris River just south of Baghdad. The Ctesiphon arch is a pointed ovoid peculiar to Mesopotamian architecture; it was built using unfired, thin mud bricks which were laid on a slant.