Cahokia: The City That Vanished

Just across the Mississippi from St. Louis, you are passing one of the most extraordinary places in North America. This is Cahokia, not the small Illinois town that shares its name, but a vast pre-Columbian city that rose and fell a thousand years before European settlers arrived.

People first lived here around seven hundred A.D., but the city truly exploded around the year one thousand and fifty. At its peak, roughly a hundred years later, Cahokia spread across four thousand acres and held a population estimated at nearly twenty thousand, larger than London at the same moment. It was the most extensive urban center in prehistoric North America north of Mexico, and the hub of a culture archaeologists call Mississippian.

The builders left behind more than a hundred earthen mounds. The largest, called Monks Mound, remains the biggest prehistoric earthwork in the Americas. At its base it is roughly the same footprint as the Great Pyramid of Giza, about nine hundred fifty feet long and seven hundred seventy-five feet wide, rising thirty meters above the floodplain. The city's ruler lived at its summit.

The builders also erected what scholars call Woodhenge: a ring of forty-eight large wooden posts precisely aligned with the sunrise on the solstices and equinoxes. At the spring and fall equinoxes, the sun rises exactly behind Monks Mound, as if the mound itself is giving birth to the sun, a celestial calendar built into the city's geography.

Then, around twelve hundred A.D., the population began to fall. By the mid-thirteen hundreds the site was fully abandoned. Why remains one of the great mysteries of American archaeology. Drought, flooding, political collapse, and disease have all been proposed; none is definitively proven.

UNESCO designated Cahokia a World Heritage Site in nineteen eighty-two. The interpretive center and reconstructed Woodhenge are open to visitors today, a reminder that North America had its own urban civilization centuries before Columbus set sail.