Cahokia at its Peak

Around 1050 AD, Cahokia, a Native American city in the Mississippi River valley near present-day St. Louis, entered its period of greatest growth. It was the largest settlement north of Mexico, and its scale, planning, and monumental architecture show that sophisticated urban societies existed in North America centuries before European contact. The summary's claim that it was larger than contemporary London is often repeated, and it is plausible for this period, though population estimates for both cities are uncertain.

The city arose in the American Bottom, a fertile floodplain just below the meeting of the Mississippi, Missouri, and Illinois rivers. Its people were part of the Mississippian cultural tradition, which grew from earlier Woodland societies and relied heavily on maize agriculture. Settlement in the area had existed for generations, but archaeologists see a sudden transformation around 1050, sometimes called the "Big Bang." Population surged, older villages were abandoned or reorganized, and a new planned center took shape. Why this happened is debated. Explanations include religious movements, political consolidation, and migration into the area, and the evidence does not settle the question.

At its height, Cahokia likely held in the range of 10,000 to 20,000 people in the city and nearby districts, with some estimates higher. Its core was a ceremonial and political center dominated by Monks Mound, a massive earthen platform of several terraces, still the largest prehistoric earthwork in the Americas. Builders moved enormous quantities of soil in baskets, and a large timber palisade was later constructed around the central precincts. The site included plazas, dozens of smaller mounds, and residential neighborhoods. Archaeologists have also found several circular timber alignments, nicknamed "Woodhenges," which may have been used to track the movement of the sun and mark seasonal ceremonies.

Cahokia was also a hub of trade and ritual. Objects found there include shell from the Gulf Coast, copper from the Great Lakes region, and distinctive stone items from far-flung sources, suggesting broad networks of exchange and influence. Burials, such as those in Mound 72, point to marked social hierarchy and ceremonial violence, including what appear to be sacrificial offerings, though interpretations vary.

The city's decline began in the 1100s and continued through the 1200s, and it was largely abandoned by about 1350. Proposed causes include flooding, overuse of timber and other resources, climate shifts, social conflict, and political instability. Most researchers think several factors combined. Cahokia left no written records, so its own name and language are unknown; "Cahokia" comes from a later Illinois-confederation group living nearby. Today the site is a UNESCO World Heritage Site and a major window into Indigenous urban life in pre-Columbian North America.