Taq Kasra, the Arch of Ctesiphon
How did Sasanian builders raise a 25-metre unreinforced brick vault to a height of 37 metres with no timber centring holding it up — and how did they arrive at a curve that European engineers only described mathematically eleven centuries later?
3rd–6th century CE (Sasanian; most often placed c. 540 CE under Khosrow I) · Ctesiphon, Salman Pak, Baghdad Governorate, IraqAdded September 2026