Cahokia Mounds, Illinois
Spread across six square miles and with an estimated population of 20,000, Cahokia was once bigger than London. Or at least, London as it was in AD 1250 when North America’s first-known city touched its peak. The land is dotted with around 80 dirt mounds, with their origins shrouded in mystery.
An interpretive center and gallery reveal what is known about the ruins, located a few miles outside Collinsville. It’s believed to have been settled around AD 600, with a series of “Woodhenges,” calendars made with red cedar posts that line up with the rising sun on certain days of the year, built by the Cahokia around AD 1100.
