Nilometers were used ever since the ancient Egyptian period, as they were portable Nilometers made of wood. Egyptian used the cubit system as a unit of measurement. The best height of water was 16 cubits (the cubit is about 54 cm.).
The Nilometer in Rawdah Island is one of the oldest existing Islamic monuments of Egypt in its original form. According to a frieze of Kufic inscription, it was built by orders of the Abbasid caliph al-Mutawakkil in 247/861.
Its main purpose was to measure the annual Nile flood in August – September to regulate distribution of water and the levy of taxes paid by Egypt to the caliph.
It’s located in the southeastern corner of al-Rawdah Island.
The Nilometer consist of a shaft communicating with the Nile through tunnels dug on three levels on its eastern side. The shaft itself is circular at the bottom and rectangular at the top and is lined with stone.
The exterior of the Nilometer is a square with a cone shaped dome.
As for the interior, the shaft has an octagonal column. The column, which has a Corinthian capital, is divided into 19 cubits and resting on a square wooden base made of palm trees.
The upper part of the inner walls have carved inscriptions in Kufic, they are Quranic texts referring to water, vegetation and prosperity.
The celebration of the Nile:
One of the famous celebrations of the Nile was wafaa el-nil (the Nile fulfill). This was when the Nile fulfilled its promise and attained the needed height. Celebrations started in June. When the water continued rising, the announcement was recorded and sent to the different provinces to get ready. During the Fatimid period, the caliph himself attended the celebration. Especial young boys were chosen to call for the daily increase in water’s height and their faces were anointed with saffron.
Later on, two other celebrations were added. The first celebration was the anoint the Nilometer, the ruler was responsible for anointing the column of the Nilometer with saffron.
The second celebration of cutting the canal was also attended by the ruler, who broke a small part of a mud brick dam with a golden axe.