Nilometer

The Nilometer was an instrument that measured the height of the Nile in Egypt. It was usually a set of steps cut into the rock beside the Nile.
Records were kept of the annual rise and ebb of the Nile which in turn affected how the level of Taxation would be set.

Records were kept from the time of the Pharaohs. Measuring the Nile enabled the Egyptian priests to announce the date of the first Nile Flood and the date of its maximum height. Taxation on agriculture was based on predicting how high the Nile would flood. On average, every fifth year, it would either be too excessive and destroy crops, or too low, and lead to drought. As it never rained in Egypt, everything depended on the Annual Flood of the Nile.

The waters of the Nile first rose as early as the beginning of June, and continued rising until September when the level stabilised for two to three weeks. The level rose once more during October, reaching its highest level, before declining to its lowest level, in June.

The Egyptians dated the Annual Rise of the Nile from the heliacal rising of Sirius. They based their four seasons around the rise and fall of the Nile. They believed the Nile rose due to the tears Isis wept for her deceased husband Osiris.
The flood waters are due to the annual heavy rains at the sources of the Blue and White Niles, and the melting snow in the Ethiopian Mountains.

A portable Nilometer consisting of a stick with heights marked off on it.
- One was kept in the Serapeum, the Temple of Serapis at Alexandria. It was ritually brought out, and used to measure each rise in the Nile waters, before being returned to the Temple. Constantine I ordered it to be placed to rest in the church of Alexandria.
A column in the river with the heights of the water marked off at intervals.
A flight of stairs leading down to the Nile with the heights marked off along the stair wall.
- This type of Nilometer exists at Elephantine Island.
A channel from the Nile through a conduit that led to a deep cylindrical well within a Temple building.
- The Temple at Kom Ombo had this type of Nilometer.
- The Temple at Philae Island had a Nilometer inside the Temple building.

Elephantine Island:
- near Aswan, it was located near the Nile Cataracts on the Frontier of the Kingdom of Kush (Sudan). It was therefore the first place in Egypt where the rise in the Nile could be recorded.
In the Temples:
- The Temple at Philae Island held a Nilometer.
- The Temple of Kom Ombo had a Nilometer inside the Temple building.
Cairo:
- Another Nilometer existed near Cairo, where the Nile rose about a week later than at Elephantine Island.
Alexandria:
- the portable Nilometer in the Temple of Serapis.
Edfu and Esna.

Elephantine Island, Egypt: