The City Under the City: Cahokia at Its Peak

Around the year eleven hundred, this stretch of bottomland east of the Mississippi River held the largest city in North America. Larger than London at the same moment. Larger than any city that would exist north of Mexico for another seven hundred years. The people who built it left no written language, so we do not know what they called it. Archaeologists call it Cahokia.

At its peak, between approximately ten fifty and thirteen fifty of the common era, the population may have reached fifteen thousand to twenty thousand people. The city was planned, not organic. It had a central plaza, a wooden post circle the researchers call Woodhenge that tracked the solstices and equinoxes, and an elite residential district separated from the commoner neighborhoods by a log stockade. The mound you can see from here, the one called Monks Mound, rises approximately one hundred feet and covers fourteen acres at its base. It is larger in base area than the Great Pyramid at Giza. It was built without metal tools, without wheels, and without draft animals, basketful of dirt at a time.

The trade network that fed Cahokia reached from the Great Lakes to the Gulf of Mexico. Archaeological evidence suggests human sacrifice at elite burial sites. Evidence also suggests sophisticated astronomical knowledge and a civic order capable of coordinating enormous construction projects across generations.

Around thirteen hundred, the population began falling. By thirteen fifty the city was effectively empty. The reasons are not settled. Drought is the leading candidate, combined with deforestation and soil depletion from agricultural intensification. Conflict may have played a role. What is clear is that a city the size of medieval London simply ceased to function within a generation or two, and the mounds were too large to reclaim. The people who built Cahokia are the ancestors of the Osage, the Quapaw, and other Siouan peoples of the region, though no living nation has been formally designated as Cahokia's direct descendant community. The mounds remained. They are why you are here.