Cahokia's Disappearance: A Vanished City

The Mississippian civilization that built Cahokia reached its peak around eleven hundred of the common era and began declining around thirteen hundred. Within fifty years it was effectively over. A city that had housed perhaps twenty thousand people was empty. The mounds remained because they were too massive to reclaim, but the people who had built them and the political and economic order they had sustained were gone.

The reasons are not established, and archaeologists are honest about that. Several factors converged. A prolonged drought in the late thirteenth century reduced agricultural yields in a city that had intensively farmed the surrounding bottomland for generations. Deforestation for construction timber and fuel had already depleted the surrounding landscape. The combination of drought and exhausted soil meant the city could no longer feed itself at scale.

Social conflict may have played a role. Evidence of stockade walls suggests the city was fortified, which implies external threat or internal instability or both. Population decline may have been gradual, families and clans leaving for other settlements as conditions worsened, rather than a single catastrophic collapse. The mounds at the center were the last things abandoned. Monks Mound was still standing in fifteen forty-one, around the time Hernando de Soto's expedition reached the Mississippi River hundreds of miles to the south, though by then the city around the mound had been gone for nearly two centuries.

The builders' descendants, if they can be identified at all, are among the Siouan peoples who occupied the Missouri and Illinois river valleys at European contact. No federally recognized tribe has been formally designated as Cahokia's direct descendent community. The site was designated a United Nations Educational, Scientific and Cultural Organization World Heritage Site in nineteen eighty-two, recognizing it as one of the most significant archaeological sites in the world.