The Sumerians were an ancient people who lived in southern Mesopotamia, in what is now southern Iraq, and their civilization flourished between around 4100 and 1750 BCE. Sumer was not a single country but a region of city-states, each with its own ruler. The Sumerians referred to themselves as "the black- headed people" and called their land simply "the land" or "the land of the black-headed people." They are credited with many major innovations, including the invention of writing (cuneiform), the creation of one of the first great civilizations, time division into hours and minutes, monumental architecture, irrigation techniques, and early governmental bureaucracy. The Sumerians settled along the fertile floodplains between the Tigris and Euphrates rivers, benefiting from rich soil and water for irrigation. Their culture thrived with advancements in farming, architecture, literature, and administration. They also produced important literary works such as the Epic of Gilgamesh. Although they were eventually absorbed by the Akkadians and later peoples, their legacy was rediscovered in the 19th century through archaeological excavation. The origins of the Sumerians are still debated, but they spoke a unique, non- Semitic language and may have come from northern Mesopotamia or nearby regions. They lived in a constellation of city-states rather than a unified kingdom, and their civilization is considered the earliest known complex society and among the cradles of civilization.