When and from where [the Sumerians] first settled near the Euphrates was much debated a generation ago, but without any clear consensus. People had settled the region and were growing crops by irrigation before 5000 BC; the best we can say is that the urbanized people who, before 3000 BC, first wrote Sumerian emerged out of this agricultural way of life and tradition without any obvious break.

Timothy Potts, in “Buried Between the Rivers”, New York Review, 9/25/2003