Once Mansur had agreed the site, it was time to embark on the design. Again we are told that this was entirely the caliph’s work. Under strict supervision he had workers trace the plans of his round city on the ground in lines of cinders. The perfect circle was a tribute to the geometric teachings of Euclid, whom he had studied and admired. He then walked through this ground-level plan, indicated his approval and ordered cotton balls soaked in naphtha (liquid petroleum) to be placed along the outlines and set alight to mark the position of the massively fortified double outer walls.
