The Nile River, one of the longest river systems in the world, begins with six cataracts that flow into a narrow valley-river section, then spreads out into the marshy Nile Delta near the Mediterranean Sea. Up to 90 percent of Egyptians live in the narrow, fertile Nile Valley.
The Blue Nile and White Nile join in central Sudan at Khartoum to form the Nile's headwaters. Downstream, the Nile enters a series of six non-navigable cataracts, or rapids. The northern section between the first and second cataracts was Lower Nubia, and between the second and sixth cataracts was Upper Nubia. Just downstream from the first cataract, the modern Nile is slowed by the Aswan Dam, but in ancient times annual floodwaters carved out a long narrow valley in the Sahara, separating Egypt's deserts into the Eastern Desert and the Libyan Desert. The Nile's deep, navigable waters flow northward into Lower Egypt, where at Cairo the Nile becomes a wide, marshy delta.
Heavy spring floodwaters from throughout central Egypt inundate the river with sediment every year, and over millennia these sediments were deposited along the river banks to create the fertile river valley. Without the wealth of mud the river brought to Egypt each year, a civilization never could have sprung up. For this reason, the historian Herodotus called Egypt the "Gift of the Nile."