Sumer emerged in the southern basin of the Tigris and Euphrates from roughly the 4th millennium BCE. Sumerian is a language isolate, with no known relatives — leaving the origins of the Sumerians themselves an open question.

What made the civilization distinctive was scale. Villages had existed everywhere for thousands of years; but between 3500 and 3100 BCE, Uruk grew into the first true city, with a population approaching 40,000. That scale demanded new institutions: a central authority to manage the canal system, a temple economy to store surplus grain, specialized craft classes, and — invented to keep the accounts — writing itself.

Sumer was never a single state. Dozens of independent city-states — each with its patron deity, ziggurat temple, and lugal ("big man," king) — lived in constant rivalry and shifting alliance. The border war between Lagash and Umma is the earliest war ever documented in writing; Eannatum's "Stele of the Vultures" records it.

The Epic of Gilgamesh came out of these cities; the flood narrative that later echoed through monotheistic scripture was first written down here. Mathematics, the calendar, law, and literature — the load-bearing concepts of all later Near Eastern civilizations — owe a great deal to Sumer. Even after political power passed to Akkad and Babylon, Sumerian endured for centuries as a sacred and scholarly language.