The Sumerians first settled in Sumer, a southern part of Mesopotamia, around 3500 BCE. Their reign ended with the rise of the Akkadians who established themselves in central Mesopotamia. They were later replaced in power by the Babylonians, who were in turn usurped by kingdoms that were relatively less powerful. Despite having already settled in the valley of the river Tigris by around 2000 BCE, the Assyrians became dominant only after 1000 BCE.