For more than a century, archaeologists have believed that ancient Mesopotamian cities – places like Uruk and Ur – were born along the banks of the great rivers of the Middle East and depended mainly on irrigation of surrounding deserts for their survival.

Dr. Jennifer Pournelle, a research assistant professor in the School of the Environment at the University of South Carolina, has a different theory. She believes that the great cities of southern Iraq grew and thrived in vast lowland marshes fed by those rivers, not along the banks of rivers themselves....