Early cave-dwelling humans were hunter-gatherers, and moved in groups from one place to another, following the path of the prey. Out of Africa, as they invented agriculture, they began to settle near fertile lands of great rivers of the world. Great civilizations flourished in Mesopotamia, Egypt, China, Persia, Mohenjo-Daro, India, Greece, Mayans, Inca, Aztecs, Rome, and so on. The rise of great civilizations was also followed by the fall of civilization throughout human history.