Nilometer (2 Al Malek Al Saleh St., Rhoda Island, Cairo) — Located on the lower end of Rhoda Island, in Cairo, the Nilometer was used to measure the level of the river in times past. The structure consists of a measuring device, or a graduated column sitting below the Nile’s level, reached by steps that curl around the chamber housing the column. If the water dropped to a low level, Cairenes would expect drought and famine; if it rose too high they could predict flood and disasters. The Nilometer is no longer functional today but it is worth a visit. Built in 861 AD by the Muslim Caliph Al-Mutawakkil, it is crowned by an interesting pointed dome that was reconstructed after being destroyed by French invaders. The building’s interior is breathtaking.