The Round City in Western Baghdad which, asKasready said, was founded by Mansur in the year 145, formed the nucleus of the great metropolis which afterwards, radiating from this centre, spread itself over both banks of the Tigris. This burgh, generally referred to as Madinat-al-Mansur or the City of Mansur, was built with a double wall and four gates, it was exactly circular in outline, and stood close to the right bank of the river, at the angle formed by the inflowing of the Sarat Canal. As the Moslem writers remark, the main feature of the City of Mansur was that it was circular, with four equidistant gates, and this was a novelty in Islam, probably derived from Persia. Any one entering the City of Mansur would, after crossing the ditch which encircled the outer wall, pass in by one of these four gates, from each of which a thoroughfare led directly to the great central area.