Sumer was an ancient civilization and historical region in southern Mesopotamia (modern Iraq) during the Chalcolithic and Early Bronze Age. Although the earliest historical records in the region do not go back much further than ca. 2900 BCE, modern historians have asserted that Sumer was first settled between ca. 4500 and 4000 BCE by a non-Semitic people, who may or may not have spoken the Sumerian language. These prehistoric people are now called "proto-Euphrateans" or "Ubaidians and are believed to have evolved from the Samarra culture of northern Mesopotamia (Assyria). The Ubaidians were the first civilizing force in Sumer, draining the marshes for agriculture, developing trade, and establishing industries: including weaving, leatherwork, metalwork, masonry, and pottery.
The Sumerian city of Eridu, on what was then the Persian Gulf, is believed to be the world's first city, where three separate cultures fused - that of peasant Ubaidian farmers, the mobile nomadic Semitic pastoralists, and fisher folk. The surplus of storable food created by this economy allowed the population of this region to settle in one place, instead of migrating as hunter gatherers. It also allowed for a much greater population density, and in turn required an extensive labor force and a division of labor with many specialized arts and crafts. Sumer was also the site of early development of writing called cuneiform .
By the late 4th millennium BCE, Sumer was divided into about a dozen independent city-states delineated by canals and other boundary makers . Each was centered on a temple dedicated to the particular patron god or goddess of the city and ruled over by a priestly governor (ensi) or by a king (lugal), who was intimately tied to the city's religious rites. The Sumerian city states rose to power during the prehistorical Ubaid and Uruk periods.
The Ubaid period is marked by a distinctive style of fine quality painted pottery which spread throughout Mesopotamia. During this time, the first settlement in southern Mesopotamia was established at Eridu by farmers who brought with them the Hadji Muhammed culture, which first pioneered irrigation agriculture. Eridu remained an important religious center when it was gradually surpassed in size by the nearby city.
The archaeological transition from the Ubaid period to the Uruk period is marked by a gradual shift from painted pottery, domestically produced on a slow wheel, to a great variety of unpainted pottery mass-produced by specialists on fast wheels. By the time of the Uruk period (ca. 4100–2900 BCE), the volume of trade goods transported along the canals and rivers of southern Mesopotamia facilitated the rise of many large, stratified, temple-centered cities where centralized administrations employed specialized workers. Artifacts, and even colonies of this Uruk civilization, have been found over a wide area—from the Taurus Mountains in Turkey, to the Mediterranean Sea in the west, and as far east as Central Iran. The Uruk period civilization, exported by Sumerian traders and colonists had an effect on all surrounding peoples, who gradually evolved their own comparable, competing economies and cultures.
In the early Sumerian period, cuneiform and pictograms suggest the abundance of pottery and other artistic traditions. Furthermore, tablets were used for writing purposes, and copper, gold, and silver were worked by the smith. Daggers with metal blades and wooden handles were worn, and copper was hammered into plates, while necklaces or collars were made of gold.
Sumerian cities during the Uruk period were probably theocratic and were most likely headed by a priest-king (ensi), assisted by a council of elders, including both men and women. It is quite possible that the later Sumerian pantheon was modeled upon this political structure. There was little evidence of institutionalized violence or professional soldiers during the Uruk period, and towns were generally unwalled. During this period, Uruk became the most urbanized city in the world, surpassing for the first time 50,000 inhabitants.
The earliest king authenticated through archaeological evidence is Enmebaragesi of Kish, whose name is also mentioned in the Gilgamesh epic—leading to the suggestion that Gilgamesh himself might have been a historical king of Uruk. As the Epic of Gilgamesh shows, this period was associated with increased violence. Cities became walled and increased in size as undefended villages in southern Mesopotamia disappeared.