The caliph’s city as a perfect circle about 2.3 km across: moat, double wall and four gates on the diagonals, a ring of houses in named streets, and at the centre an empty court with only the palace of the Green Dome and the Friday mosque. The markets lie outside, in al-Karkh.
In 762 the second Abbasid caliph, al-Mansur, chose a site on the west bank of the Tigris where the Sarat canal joined it, and built a new capital, the City of Peace. The chroniclers say he had its plan traced on the ground in lines of ash, walked it, and then had the lines soaked in naphtha and set alight so that he could see it whole. It was round (an old idea in the Near East, with Parthian and Sasanian precedents), so that no part lay further from the ruler than any other. A moat, an outer wall, an open intervallum and a massive main wall with over a hundred towers surrounded it; four gates, each named after the region its road led to, stood at equal intervals round the circle, reached through bent passages and crowned by domed chambers.
Inside the main wall a ring of houses was divided into quarters by the four gate avenues, which were lined with arcades. The land was granted to the caliph’s commanders and clients, and each street (sikka) bore the name of its holder and could be closed at night. A third wall separated the houses from the vast central court, where nothing stood but the caliph’s palace (its Green Dome eighty cubits high, visible from the whole city), the Friday mosque built against it, and the guard, the police and the offices of state round the edge. In 773, fearing the crowds and the strangers that trade brought within the walls, al-Mansur moved the markets out to al-Karkh in the south, giving each trade its own street.
Nothing of the Round City survives; it was absorbed into the growing metropolis within a century and has vanished under modern Baghdad. This model follows the descriptions of al-Ya‘qubi (891) and al-Khatib al-Baghdadi (eleventh century) as reconstructed by modern scholars; all dimensions are rounded, and the number of streets, the depth of the residential ring and the arrangement of the court are editorial. Click any building to see which rule placed it.