Nilometers were structures that measured the clarity and water level of the Nile River during flood seasons long before the construction of the Aswan Dam. There are three kinds of nilometers, the simplest comprising a tall column erected inside a stone structure called a stilling well such as the one on Rhoda Island in Cairo. Built in 861, the Rhoda nilometer contains an octagonal marble column supported by a wooden beam. A staircase spirals down the stilling well, and a finely ornamented conic dome covers the structure.
Nilometers were in use as early as 5,000 years ago, and only the priests and rulers could monitor the water level. Accordingly, their ability to mysteriously predict the Nile’s behavior impressed the common people. For this reason, they built several nilometers in temples to collect more tax.
Another nilometer design involved a flight of stairs into the water with depth markings along the way. The most famous example of this kind is located on the island of Elephantine in Aswan. Meanwhile, the most complex nilometer design involves a channel leading water from the riverbank to a cistern or a well like the one in the Kom Ombo Temple.
