SHARE For 800 years, the ancient city of Ctesiphon served as a capital to the Parthian and the Sasanian empires. Sitting alongside the Tigris, south-east of present-day Baghdad, the city was one of the richest of its day, with a palace extravagantly decorated in marble, glass mosaics and jewel-adorned carpets. Connecting two wings of this royal complex was an enormous parabolic arch, made of bricks and mortar, measuring 37 metres tall and 48 metres long. Even today, 1,700 years later, it is still the largest single-span bridge in the world. But that impressive record might be nearing its end. Bit by bit, the Arch of Ctesiphon, or Taq Kasra, is falling down. The culprit isn’t conflict or looting – typical suspects for most Iraqi heritage sites under threat – but sustained neglect and climate change. Substantial portions fell in 2019 and 2020, and last month, after 20 days of torrential rain, a sizeable chunk dropped into a heap of rubble.