A city bigger than London stood across from St. Louis
Around 1100, Cahokia may have housed more people than London or Paris — and almost nobody outside archaeology knows its name.
Directly across the Mississippi from present-day St. Louis, a city once covered about six square miles, ringed by more than a hundred earthen mounds, some of them taller than a ten-story building. At its peak around 1100 AD, by the higher estimates archaeologists have proposed, Cahokia's population may have exceeded that of London or Paris in the same century.
No one alive knows what its residents called it. "Cahokia" is a name French explorers borrowed centuries later from an unrelated Illiniwek group that happened to be living nearby when the city was already an overgrown ruin.
The builders raised the mounds without wheels, without draft animals, without metal tools — basket by basket of earth, carried by hand over generations, to build a skyline that briefly rivaled anything in Europe. Then, sometime in the 1300s, the city emptied out. Historians point to drought, deforestation, and political strain, though the full account of why tens of thousands of people simply left is still being pieced together.
It would be nearly five hundred years before another city in what's now the United States held as many people. The Gateway Arch stands a few miles from where it happened, pointed the wrong way to notice.