Sumer, located in southern Mesopotamia (now South Central Iraq), is the earliest known civilization, emerging between the 6th and 5th millennium BC. It is one of the cradles of civilization along with Egypt and the Indus Valley. Sumerian farmers grew an abundance of grain and other crops, which enabled them to form urban settlements. The Sumerians were the people of southern Mesopotamia whose civilization flourished between 4100 and 1750 BCE.

Sumer was never a cohesive political entity but a region of city-states, each with its own king. The country was the site of at least 12 separate city-states, each comprising a walled city and its surrounding villages and land, and each worshiping its own deity. The Sumerians essentially invented time by dividing day and night into 12-hour periods, hours into 60 minutes, and minutes into 60 seconds. They also left the world a number of technological and cultural contributions, including the first schools, the earliest version of the tale of the great flood and other biblical narratives, the oldest heroic epic, governmental bureaucracy, monumental architecture, and irrigation techniques. The Sumerian civilization laid the foundation for many aspects of human society from language and writing systems to complex urban centers.