Egypt, which produced the world’s first great organised society, lies to the north-east of the continent of Africa. It is bounded to the north by the Mediterranean, the south by the First Cataract and to east and west by large tracts of barren desert. The Western or Libyan Desert and the Eastern or Arabian Desert are separated by the River Nile, which emerges from the lakes of equatorial Africa and flows over 4,100 miles to the sea. Ranking with the Amazon and the Congo as one of the three longest rivers in the world, the Nile cascades over Egypt’s granite threshold at Elephantine, flows through Upper Egypt, the area lying between Aswan and modern Cairo and then, 201 miles before it reaches the sea, it fans out in a fertile triangle, the Delta, or Lower Egypt. The Egyptian Nile is the vital artery' linking Upper and Lower Egypt. It is also the cause of the great productivity of the Egyptian soil, for it annually brings a copious deposit of rich silt from the monsoon-swept tableland of Ethiopia. Since rainfall in Egypt is almost non-existent and the people are entirely dependent on the river for their crops, it was ultimately on the fertility of the soil that the Egyptian civilisation was based.
In the period known as the Late Paleolithic, large areas of Egypt were covered with forests and savanna. The Egyptian Nile River, as yet unharnessed, was an alien force. For eons of time it had poured its heavily charged waters over the land. Only the plateau to the west and the mountain range to the east halted its dispersion and accommodated its agitating fury. The distance between them was an average of 8 miles and the river left traces of its action in the wearing of rocks and in the colour of its silt on either side. During the protracted climatic fluctuations when the rainfall in Ethiopia lessened, the river flowed with less turbulence and slowly carved its channel. A rich earthy sediment was deposited on each side of the river. The surplus was borne to the north where ceaseless accumulation over tens of thousands of years transformed what was once a bay into a vast triangular morass that formed the Delta.