Four rivers and three major river valleys that were the centers of ancient civilizations were part of Alexander's dominion: the Indus River to the east was a center of the eponymous ancient civilization that was later conquered by a nomadic tribe that called themselves Aryans. The Tigris and the Euphrates together constituted a valley in the Middle East that was the center of Mesopotamian civilization. Finally, the Nile valley was the cradle of ancient Egyptian civilization. All these were bronze-age civilizations. They were conquered and vanished with the advent of numerous nomad tribes.
