Archaeologists try to find out why flourishing Metropolis was abandoned

November 16, 2021

East of the Mississippi River in Illinois lie the remains of an American Indian metropolis: the Cahokia Mounds. This urban center occupied nearly 4,000 acres during its peak between A.D. 1000 and the 1200s. Cahokia’s inhabitants built scores of burial mounds, public buildings, and even an astronomical observatory.

Cahokia Mounds stands at the center of what was once the greatest civilization between the deserts of Mexico and the North American Arctic.

The site of one of North America’s first cities and arguably one of American Indians’ finest achievements, it is the most visible example left today of the Mississippian culture, an agricultural civilization that spread across the U.S. Midwest and Southeast starting around A.D. 800 and peaking around the 13th century.

Cahokia is more than just an occasional meeting spot for scattered tribes. Nearly everywhere archaeologists dug, archaeologists found homes—indicating that thousands of people had once formed a community there— and many of their homes were built in a very brief span of time.

Research revealed that the whole city seemed to have sprung to life almost overnight around 1050. People streamed in from surrounding areas, building houses and the infrastructure of a new city—including several mounds with buildings on top and a grand plaza the size of 45 football fields.

As many as 15,000 people lived in Cahokia at its peak, some estimate, but by 1400 the city was deserted. Cahokia’s demise is perhaps an even greater mystery than its emergence. Historians note that the city grew to prominence during an especially favorable climate phase and began shrinking around the time the climate became cooler, drier, and less predictable.

In 2021 geoarchaeologist Caitlin Rankin turned that idea on its head. She published her findings in the journal Geoarchaeology, showing that it was impossible for deforestation and flooding to cause the city’s demise. Rankin’s excavations at the site found no evidence of flooding during Cahokia’s occupation.

As scholars look to other explanations, some are examining if increased conflict among different groups caused the city to decline. Others are looking to see if a major drought in the region could have led the Cahokia people to seek more fertile lands and leave their city behind.