Cahokia’s Mounds
Near modern St. Louis, this 1,200-year-old Native American metropolis contains massive earthworks, indicating a complex society that mysteriously disappeared. Monks Mound towers 100 feet high, surrounded by 120 smaller mounds across 6 square miles. The settlement flourished between 900-1200 AD with wooden astronomical henges and extensive corn cultivation. Its population reached 20,000 people, rivaling medieval London in size. The civilization abruptly declined by 1350 AD, possibly due to climate change.
