Sumer (from Akkadian Šumeru; approximately, "land of the civilized lords" or "native land") is a 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.

2500 BCE, modern historians have asserted that Sumer was first settled between ca.

4500 and 4000 BCE by a non-Semitic people who possibly did not speak the Sumerian language (pointing to the names of cities, rivers, basic occupations, etc.

as evidence).These conjectured, prehistoric people are now called "proto-Euphrateans" or "Ubaidians" and are theorized to have evolved from the Samarra culture of northern Mesopotamia.

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.

However, some, such as Piotr Michalowski and Gerd Steiner, contest the idea of a Proto-Euphratean language or one substrate language.Sumerian civilization takes form in the Uruk period (4th millennium BCE), continuing into the Jemdat Nasr and Early Dynastic periods.

It is conquered by the Semitic-speaking kings of the Akkadian Empire around 2270 BCE (short chronology).

Native Sumerian rule re-emerges for about a century in the third dynasty of Ur (Sumerian Renaissance) of the 21st to 20th centuries BCE.

The cities of Sumer are the first civilization to practice intensive, year-round agriculture, by perhaps c. 5000 BCE showing the use of core agricultural techniques, including large-scale intensive cultivation of land, mono-cropping, organized irrigation, and the use of a specialized labor force.

The surplus of storable food created by this economy allows the population to settle in one place, instead of migrating after crops and grazing land.

It also allows for a much greater population density, and in turn requires an extensive labor force and division of labor.

Sumer is also the site of early development of writing, progressing from a stage of proto-writing in the mid 4th millennium BCE to writing proper in the third millennium.