In 1967, an archaeologist was excavating a giant, ancient city in the middle of Illinois.

What Cahokia may have looked like at its peak. Painting by William R. Iseminger/Cahokia Mounds State Historic Site.

The city, called Cahokia, existed from about 600 A.D. to about 1300 A.D. and is located across the river from modern St. Louis. It was massive; no other city in the contiguous United States would rival it until the 1800s.

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