Abstract: In the Near East, farming started in the Levant and northern Mesopotamia and, by 9,000 BP, was established across much of the region. Farming villages grew into towns that gradually increased in size and techno-social complexity. This development was punctuated by at least three serious aridification events in 8,200, 5,200, and 4,200 BP that led to the partial abandonment of rainfed farming and dramatic reductions in social complexity. A momentous development was the invention of irrigation by the Samarrans after 8,000 BP. This allowed the colonization of southern Mesopotamia and the evolution of the first true urban cultures in Sumerian centres such as Ur and Uruk. Sumerian agriculture was dominated by intensively farmed barley monocultures controlled by elites who developed writing, organized warfare, imperialism, and ruled over an increasingly coercively managed subject population.

Keywords: climatic events, aridification, 4200 BP, Abu Hureyra, barley, Uruk, Ur, writing, Sumer, Mesopotamia, societal collapse,