Nilometer of Rawda Island, Cairo

The Nilometer is an Abbasid structure on Rawda Island in Cairo, commissioned by the caliph al-Mutawakkil and built by Ahmad ibn Muhammad al-Hasib in 862. ¹ Yeomans counts it the earliest surviving Islamic monument in Egypt, one of Cairo's finest structures, and a disciplined example of the principle of fitness for purpose. ¹

The Nilometer measured the height of the Nile waters during the annual flood, and its readings were essential in setting irrigation policy. ¹

It is a stone-lined pit, circular at the bottom and rectangular at the top, linked to the Nile on its east side by three lateral tunnels at different levels. ² Twenty-four steps lead down to a landing facing four recessed pointed arches framed by colonnettes; Yeomans notes that they are identical in form to the arches Gothic architects used three centuries later. ²

At the centre of the pit stands an octagonal marble measuring column with a composite capital, held at the top by a timber beam and set at the bottom in a granite millstone; a modern wooden dome covers the whole. ² The column is divided into nineteen cubits, and the sixteenth-cubit mark stands for the ideal flood level. ²

Ahmad ibn Tulun restored the Nilometer in 872-873 and removed the caliph al-Mutawakkil's name from a band of Kufic inscription; Yeomans reads this as a wish to dissociate himself and Egypt from the Abbasid caliphate. ² The restoration was one of Ibn Tulun's hydraulic projects, which also included dredging Alexandria's canal and the Aqueduct of Basatin that carried water to al-Qata'i. ¹