Saturday, October 25, 2025

The Tidal Trigger: How Bottom-Up Irrigation Fueled the Sumerian State

by Mary Harrsch © 2025

“Seven thousand years ago, twice-daily tides in the shallow, narrow Persian Gulf would have pushed saltwater up the Tigris and Euphrates, forcing freshwater back the way it came.

As tides move up the river, “saltwater is heavier than fresh, so it stays at the bottom and lifts the freshwater up,” says Liviu Giosan, co-author of a new paper on the study of deep soil samples from ancient Lagash . “When you have water rising twice a day, you can tap it for agriculture very easily.”

Even far from the coast, communities would have been able to see a regular rise and fall in the river’s level and divert it to water wheat fields, date palm groves, and vegetable gardens, paving the runway for what scholars sometimes call the “Mesopotamian takeoff.” As populations grew and settled, the river kept bringing fresh soil and sediment downstream as part of annual spring floods, opening new, rich farmland.

These Ubaid 4 Period female figurines (c. 4500 BCE) discovered at Ur with their stylized features and emphasis on fertility, materialize the religious worldview of the early Mesopotamian farmers who harnessed the tides. They represent the deep-rooted, pre-state spiritual traditions that would later be formalized into the Sumerian pantheon. Photographed at the Penn Museum in Philadelphia, PA by the author.

Archaeologist Jennifer Pournelle points out the findings upend the idea that cities arose from huge state-organized infrastructural projects but instead developed naturally as people settled next to each other to let the Tigris nourish their crops. This article, using findings in Giosan et al’s research, that appeared in the online journal Science makes the case for tidal irrigation being the trigger for state formation in ancient Mesopotamia. But it stops short of explaining the subsequent steps in state development.

https://www.science.org/content/article/sumerian-civilization-may-have-been-jump-started-rise-and-fall-tides

However, I propose as irrigation produced surplus, elites arose to manage the distribution of the surplus, both within the community and with external partners, forming an early network of economic and social dependences. These activities generated the need for more specialists including soldiers, artisans, administrators and traders. To legitimize their authority, elite administrators also begin to intertwine their efforts with priests or shamans of existing deeply-rooted religious beliefs, thereby organizing religion to facilitate cooperation of the populace to fund tax systems used to pay standing armies and finance large-scale canal projects when tidal forces begin to diminish.

Scholars like archaeologist Stephanie Rost argue that irrigation, while important, could not have been the sole cause. She suggests the wetlands' natural wealth (fish, birds, reeds, etc.) might have been sufficient on its own to support early urbanism. But, could these activities have produced the amount of surplus requiring the rise of administrators and other specialists to manage its distribution across a wide area?

The new evidence from the Lagash core provides a elegant, bottom-up mechanism for how that surplus could have been achieved before kings and bureaucracies.

Since my research has indicated the rise of surplus administrators also leads to development of religion as a behavioral tool to manage the laboring population, I was curious if archaeologist have found evidence of early developing religion during the time period covered by the core samples. This era is termed the early Ubaid Period (c. 6500-3800 BCE). The first permanent, large villages established in southern Mesopotamia have been found to contain the earliest known temple structures in the region, like the one at Eridu. These early temples were small, single-room structures, but they were rebuilt and enlarged over centuries on the same sacred spot, showing a long-standing and deepening religious tradition.

Numerous stylized, clay figurines have been found, often with reptilian or abstract features, and frequently female. They often have applied bitumen "hair" and clay pellets for shoulders. Their exact meaning is debated, but they are widely interpreted as representing a mother goddess or a fertility deity—a concept directly linked to the concerns of an agricultural society dependent on water and land fertility. "Ophidian" (snake-like) figurines are also common finds, male figurines with elongated heads and a snake-like appearance. These may be precursors to later gods of water, wisdom, or the underworld.

Scholars assume the religion of this tidal period was likely animistic and centered on fertility and the forces of nature. The construction of temples suggests a developing communal investment in a shared belief system, and the figurines represent a conceptualization of divine forces that were critical to their survival—forces that would later be formalized into the gods Enki (god of fresh water and wisdom) and Inanna (goddess of fertility and love).

The development of religion appears to mirror the development of the state itself. It began as a localized, bottom-up set of beliefs centered on natural forces (fertility, water) that were vital to the tidal agricultural system. As society became more complex and faced environmental and social challenges, this religious system became more formalized, hierarchical, and integrated with political power, eventually producing the iconic art and inscriptions of the classic Sumerian state.

References:

Adams, R. McC. (1981). Heartland of cities: Surveys of ancient settlement and land use on the central floodplain of the Euphrates. University of Chicago Press.

Carter, R. A., & Philip, G. (Eds.). (2010). Beyond the Ubaid: Transformation and integration in the late prehistoric societies of the Middle East. The Oriental Institute of the University of Chicago.

Childe, V. G. (1950). The urban revolution. The Town Planning Review, 21(1), 3–17. https://doi.org/10.3828/tpr.21.1.k853061t614q42qh

Giosan, L., & Goodman, R. (2025). Morphodynamic foundations of Sumer. PLOS ONE, 20(8), e0329084. https://doi.org/10.1371/journal.pone.0329084

Oates, J. (1960). Ur and Eridu: The prehistory. Iraq, 22(1/2), 32–50. https://doi.org/10.2307/4199667

Service, E. R. (1975). Origins of the state and civilization: The process of cultural evolution. W. W. Norton & Company.

Stein, G. J. (1994). Economy, ritual, and power in 'Ubaid Mesopotamia. In G. Stein & M. S. Rothman (Eds.), Chiefdoms and early states in the Near East: The organizational dynamics of complexity (pp. 35–46). Prehistory Press.

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