“These results confirm that there was more than one path to early urbanization,” said Weiss, a Professor of Near Eastern Archaeology at the Yale School of Forestry & Environmental Studies and the Department of Near Eastern Languages & Civilizations. “In fact, there was a second and far more widely distributed pathway.”



The results validate a long-held hypothesis promoted by Weiss that suggests that the earliest cities of northern and southern Mesopotamia were supported by two distinct agricultural systems.



“So from the very beginning settled human life was operating on very different environmental bases in northern and southern Mesopotamia,” said Gil Stein, another co-author who is professor of archaeology and Director of the Oriental Institute at the University of Chicago. He is also one of Weiss’s former students at Yale.



“Just think of how interesting that is: even though the ecology and agricultural systems were so totally different — and with different organizational requirements — these cities developed in parallel even as they operated on different principles. And Harvey was one of the first people to point this out in a very clear and incisive way.”



While the early cities of northern Mesopotamia were able to utilize extensive agriculture because the rain-fed climate allowed them to, Weiss says, this reliance on rainfall also made them vulnerable to regular periods of drought.



In previous research he has written that this vulnerability ultimately doomed the Akkadian empire when a prolonged mega-drought struck northern Mesopotamia in the third millennium BC. Other research has shown that shorter droughts are actually typical in the region, including the one that contributed to today’s Syrian conflict.



For the new study published in Nature Plants, led by Amy K. Styring at the University of Oxford, researchers analyzed carbonized crops from Tell Leilan — which are kept at Yale University — and from the sites of Tell Sabi Abyad, Tell Zeidan, Hamoukar, and Tell Brak. All sites are located in the Khabur and Balikh drainage basins in northern Mesopotamia and all date from 6500 to 2200 BC.



While the researchers say the shift toward lower-input, extensive farming in these early cities most likely developed at household levels, it eventually led to broader socio-economic changes. “The increased importance of land-based wealth constituted a key potential source of political power,” the co-authors write, “providing the possibility for greater bureaucratic control and contributing to the wider societal changes that accompanied urbanization.”