Both Civilizations rose next to rivers. The Egyptian next to the Nile and Mesopotamian between the branches of the Tigris and Euphrates.
In both cases you have fertile land which was sometimes covered by the waters of the overflowing streams and left it when they withdraw ready for cultivation.The fact that food could be produced easily and abundantly left time for other occupations and so made both civilizations grow enormously in wealth and population. If food is available people flock to that spot and bring their particular knowledge with them.
This is how they developed into the first of the Ancients.
