1. Cahokia Mounds (Illinois)
Cahokia Mounds, located near Collinsville, Illinois, was the largest pre-Columbian settlement north of Mexico, thriving from approximately 700 to 1400 AD. At its peak, the city covered nearly six square miles and was home to an estimated 10,000 to 20,000 people, making it larger than London at the time. The site features over 70 preserved mounds, including Monks Mound, the largest prehistoric earthen structure in the Americas, standing 100 feet tall and covering 14 acres at its base. Designated a UNESCO World Heritage Site in 1982, Cahokia Mounds offers visitors a glimpse into the sophisticated urban planning and cultural achievements of the Mississippian civilization. (cahokia.heritagesites.org)
