This American Indian metropolis was mysteriously abandoned. Archaeologists want to know why.

Cahokia was a robust economic and cultural center for the Mississippian people. They built hundreds of massive mounds but suddenly left the city in the 1300s.

Built from an estimated 22 million cubic feet of earth and standing about 100 feet high, Monks Mound is the tallest structure at the Cahokia Mounds State Historic Site.
Ira Block/National Geographic Image Collection

East of the Mississippi River in southern 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, “Woodhenge,” whose wood posts aligned with the sun throughout the year. Dominating the landscape then, as it does now, was Monks Mound—the largest earthwork north of Mexico. Its four terraces soared about 100 feet high.

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.

Today the site is an Illinois state historic site, a national historic landmark, and a UNESCO World Heritage site. Nevertheless, until recently it was largely familiar mostly to people around St. Louis, Missouri. That ignorance has deep roots. The first white person to have written a detailed account of Cahokia’s mounds was Henry M. Brackenridge, a lawyer and amateur historian who came upon the site and its massive central mound while exploring the surrounding prairie in 1811.“I was struck with a degree of astonishment, not unlike that which is experienced in contemplating the Egyptian pyramids,” he wrote about the 100-plus mounds he counted. “What a stupendous pile of earth! To heap up such a mass must have required years, and the labors of thousands.”

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