Nilometer

Ancient stone column on Rhoda Island used for millennia to measure the Nile's flood level

The Nilometer on Rhoda Island, in the southern Nile, is one of the oldest intact Islamic structures in Egypt, dating from 861 AD though built on the site of earlier Pharaonic and Byzantine measuring devices. It consists of a graduated octagonal column in a pit connected by tunnel to the Nile, so that the water level could be read precisely each year.

The Nilometer gave rulers of Egypt for 3,000 years the data they needed to manage agriculture, taxation, and irrigation. It was used continuously until the construction of the Aswan dams in the 20th century made the annual flood predictable and, eventually, impossible.

The structure is small and takes only 20 minutes to visit, but it's evocative — standing in the pit beside the ancient column, you can feel the weight of all those thousands of years of river-watching. Rhoda Island is reached by bridge from the Maadi neighbourhood.

things to do sight museum
A story
The Nilometer on Rhoda Island was used for thousands of years to measure the annual Nile flood. A good flood — somewhere between 16 and 24 cubits on the graduated column — meant a productive harvest and prosperity; too low meant drought and famine; too high meant catastrophic flooding. The measurements were so economically critical that they were kept secret by the state, and the priest who read the level was sworn to reveal it only to the ruler. Tax rates were set according to the flood level.