Founded in 762 by the Abbasid caliph al-Mansur, the Round City of Baghdad was the new capital of the Abbasid Caliphate, laid out as a precisely circular walled enclosure on the Tigris. Concentric rings of walls enclosed residential quarters, with four equidistant gates linked by axial roads converging on a central precinct holding the caliph's palace and the great mosque. The geometry expressed the centrality and authority of the ruler, while the gates oriented the city to the roads of the empire. It was reportedly built by tens of thousands of workers within a few years.
It was the most ambitious ideal-geometry city of the medieval world and the administrative heart of a flourishing Islamic civilisation. Baghdad grew into a leading centre of trade, scholarship and translation before its destruction by the Mongols in 1258.