Joseph's Well (Bir Yusuf), Cairo Citadel

Joseph's Well, in the western enclosure of the Cairo Citadel, is attributed to Salah al-Din, though Yeomans thinks it probably existed in Fatimid times and was enlarged by him; it is in any case the only possible work of his on the western side of the Citadel. ^{2 1}

The double-shafted well is cut 87 metres through the limestone to the water table, a remarkable piece of hydraulic engineering in Yeomans's view. ¹ Ibn Abd al-Zahir (1223-1292) described cattle turning at the top to raise water from a reservoir halfway down, where other cattle raised it from the depths, with a path for the cattle down to the spring, all cut in the rock with no masonry. ¹ The spiral ramp down which the cattle went was lit from the inner shaft by pairs of windows. ¹

It was not the only source: there were other wells and cisterns on the Citadel, and Behrens-Abouseif notes that Salah al-Din built an aqueduct that carried and raised Nile water with waterwheels. ¹