About ten thousand years ago, the people of this area began the agricultural revolution. Instead of hunting and gathering their food, they domesticated plants and animals, beginning with the sheep. They lived in houses built from reeds or mud-brick, grouped in villages where they tended their crops. They built granaries to store their grain, and they began developing a token system to record trade and accounts.
Between 3500 and 3000, for reasons still not well understood, the civilization of Southern Mesopotamia underwent a sudden growth and change, centered in the cities of Ur and Uruk. This development was perhaps driven by climatic change which rendered the old ways of agriculture less productive. People clustered into fewer, but larger, locations and the plough, potter's wheel and the introduction of bronze can be seen as responses to the demands of a more intensive economic life, and also as causes of increased complexity in that life. In this same period came the beginnings of writing, metrological systems and arithmetic.
The main part of the third millennium, now called the Early Dynastic period, saw the gradual development of Sumerian civilization, based on numerous city states. From the Early Dynastic period comes the earliest Sumerian literature, including the epic poetry about Gilgamesh. The Sumerians lived in a complex, unpredictable and frequently hostile environment. They had to contend with floods, droughts, storms, dust, heat, disease and death. They strove to uncover order and organization in the world to overcome feelings of futility and powerlessness.
The Early Dynastic period was brought to an end when Sargon (2334-2279) created the world's