A delta is a low-elevation plain where sediment is deposited at the mouth of a river. Deltas occur in 3 general shapes:

• the "bird foot delta" made up of projections of tributaries as they flow toward the sea e.g. the Mississippi Delta in the United States.
  
• the "cuspate delta" which has cusps or "horns" extending from the river channel e.g. the Tiber Delta in Italy.
  
• the "arcuate delta" which is triangular in shape e.g. the Nile Delta in Egypt. The English word delta is derived from the Greek letter delta which is shaped like a triangle.

The Nile is the world's longest river. It begins south of the equator in the north-central section of the African continent where its principal flow is known as the White Nile. It then travels an incredible 4,130 miles (6,645 kilometers) before arriving at its terminus in the vast triangle-shaped Nile Delta in northern Egypt. The delta region, north of Cairo, then drains into The Mediterranean Sea.

In ancient times the Nile Delta was recorded as having seven tributaries, however the flow has been controlled so that now there are only two main branches, the Damietta and Rosetta (where the Rosetta Stone was found).

The Nile Delta measures approximately 100 miles / 160 kilometers north to south, and 150 miles / 240 kilometers east to west at its widest in the north. The rich silt soil of the Nile delta is the most fertile in all Africa. Whereas in many places in the world the topsoil is measured in mere inches, in the Nile Delta is varies from 50 to 75 feet in depth.