River-Valley Civilizations 3500–1500 b.c.e. The earliest complex societies arose in the floodplains of large rivers: in the fourth millennium b.c.e. in the valley of the Tigris and Euphrates Rivers in Mesopotamia and the Nile River in Egypt, in the third millennium b.c.e. in the valley of the Indus River in Pakistan, and in the second millennium b.c.e. in the valley of the Yellow River in China...
