Study: What May Have Doomed America's 'First City'

Massive floods may have led to demise of Cahokia, site of modern St. Louis
By John Johnson,  Newser Staff
Posted May 19, 2015 3:46 PM CDT
Updated May 23, 2015 7:00 PM CDT
Study May Solve Riddle of Ancient City's Downfall
File photo of the Mississippi River flowing past the Gateway Arch in St. Louis. The Cahokia civilization existed near the site of the modern city.   (AP Photo/Jeff Roberson, File)

For Native Americans living in the 12th century, Cahokia was the place to be. Now researchers think they've uncovered a major reason why the hub located near what is now St. Louis disappeared—massive flooding of the Mississippi River. Researchers dug up soil samples from two local lakes and found telltale evidence of catastrophic flooding around the time that Cahokia was flourishing. “We’re talking big floods, once a century,” a researcher from the University of Wisconsin-Madison tells the St. Louis Post-Dispatch. It seems that the region enjoyed an unusually flood-free period from roughly 600AD to 1200AD. In that time, people flocked to the fertile region, turning Cahokia into what National Geographic calls the "largest prehistoric settlement in the United States." (Another National Geographic piece frames it as "America's first city.")

But they may have gotten too complacent. People began moving from higher elevations into what we now know to be a flood plain, and the population boomed with the cultivation of maize. It peaked around the mid-12th century, but the resumption of regular floods appeared to begin taking a toll. By about 1350, the city had been abandoned. Previous theories on its demise have focused on deforestation, overhunting, political volatility, and, especially, drought. “We are not arguing against the role of drought in Cahokia’s decline, but this presents another piece of information,” says the lead author of the study at the university. Another researcher suggests the flooding could have been the final straw. “It would have had a particularly destabilizing effect after hundreds of years without large floods." (Maybe an ancient brewery would have helped?)

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