Sumerologist Samuel Noah Kramer asserts "No people has contributed more to the culture of mankind than the Sumerians" and yet it is only comparatively recently that we have built up a knowledge of the existence of this ancient culture. Sumerian civilization took form in the Uruk period (4th millennium BC), continuing into the Jemdat Nasr and Early Dynastic periods. During the 3rd millennium BC, a close cultural symbiosis developed between the Sumerians (who spoke a Language Isolate) and the Semitic Akkadian speakers, which included widespread bilingualism. The influence of Sumerian on Akkadian (and vice versa) is evident in all areas, from lexical borrowing on a massive scale, to syntactic, morphological, and phonological convergence. This has prompted scholars to refer to Sumerian and Akkadian in the 3rd millennium BC as a sprachbund. Sumer was conquered by the Semitic-speaking kings of the Akkadian Empire around 2270 BC (short chronology), but Sumerian continued as a sacred language. Native Sumerian rule re-emerged for about a century in the Third Dynasty of Ur (Sumerian Renaissance) of the 21st to 20th centuries BC, but the Akkadian language also remained in use. The Sumerian city of Eridu, on the coast of the Persian Gulf, was the world's first city, where three separate cultures fused - that of peasant Ubaidian farmers, living in mud-brick huts and practicing irrigation; that of mobile nomadic Semitic pastoralists living in black tents and following herds of sheep and goats; and that of fisher folk, living in reed huts in the marshlands, who may have been the ancestors of the Sumerians.
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 labour force and division of labour with many specialised arts and crafts. At the same time, over use of the irrigated soils led to progressive salinisation, and a Malthusian crisis which led to depopulation of the Sumerian region over time, leading to its progressive eclipse by the Akkadians of middle Mesopotamia.