An ancient country of southern Mesopotamia in present-day southern Iraq. Archaeological evidence dates the beginnings of Sumer to the fifth millennium BC. By 3000 a flourishing civilization existed, which gradually exerted power over the surrounding area and culminated in the Akkadian dynasty, founded c. 2300 by Sargon I. Sumer declined after 2000 and was later absorbed by Babylonia and Assyria. The Sumerians are believed to have invented the cuneiform system of writing.