Until the Aswan High Dam was built, Egypt received a yearly
inundation - an annual flood - of the Nile. The ancient
Egyptians did not realise this, but the flood came due to the
heavy summer rains in the Ethiopian highlands, swelling the
different tributaries and other rivers that joined and became
the Nile. This happened yearly, between June and September, in a
season the Egyptians called akhet - the inundation. This was
seen by the Egyptians as a yearly coming of the god Hapi,
bringing fertility to the land. The first signs of the
inundation were seen at Aswan by the end of June, reaching its
swelling to its fullest at Cairo by September. The flood would
then decrease in size around two weeks later, leaving behind a
deposit of rich, black silt. The amount of silt left behind due
to the height of the Nile determined the amount of crops that
the Egyptians could grow - if the inundation was too low, it
would be a year of famine. The Egyptians learned a method of
measuring the height of the Nile known as the Ni