Across the Mississippi River from St. Louis are a series of grassy mounds that seem rather out-of-place in the otherwise flat Missouri terrain. These mounds, obviously built by an incredible amount of human labor, are most of what remains of what was once a thriving metropolis back in the Middle Ages. We don’t know what the thousands of Native Americans who lived here called their great city, but it’s now known as Cahokia. In its heyday it was the largest city in North America, with possibly as many as 40,000 residents. No North American city would achieve that many residents until Philadelphia in the late 1700s, centuries after Cahokia was abandoned and reduced to the grassy mounds on which it once stood.

At its peak in the 13th century, Cahokia must have been an amazing and magnificent place. Atop the tallest mound, which has been named Monk’s Mound, stood a large wooden building that may have been a temple of some kind, perhaps the residence of a high priest or other authority figure. There was a grand plaza south of the Monk’s Mound which was a place of ceremonial functions, public meetings and games. The plaza was the size of 45 football fields, and it was definitely a sports center, much of the time. The most important game played there, which had ceremonial significance, was called chunkey. Essentially, all the functions of a major pre-modern city were present in Cahokia, from residential homes to monumental architecture and public spaces. Cahokia may indeed have resembled, in some respects, the city of Tenochtitlan, the magnificent capital of the Aztecs in central Mexico.

cahokia 2010

These mounds, looking like a public park, are all that’s left of the largest city in medieval America.

Many, many people lived in Cahokia. Archaeologists digging into the mounds have found evidence of thousands of individual houses. A lot of people came to the city very suddenly, about 1050 CE, for reasons historians don’t understand. The residents of Cahokia were what we now call the Mississippian peoples, who unfortunately didn’t develop a written language–thus we have no record of why they came, the structure of their society or what their lives in the city were like.

We do know there was human sacrifice in Cahokia. Archaeologists found a large burial mound on top of which was a “Woodhenge,” a circle of timbers that appeared arranged in monumental fashion. Underneath was the tomb of a man whose body was laid out on a bed of shell beads in the shape of a bird–hence, the man came to be known as the “Birdman.” It’s not clear why he was accorded this status other than he must have been very important, a ruler or religious figure of some kind. About 250 people were buried with him, and over half seem to have been killed by some kind of violence. Most harrowing of all, some of these skeletons were poised as if they were trying to crawl out of their graves–indicating they were buried alive. About 50 women, all around 21 years old, were killed as sacrifices for the Birdman’s burial.

Cahokia at its height must have been impressive, but at some point it began to decline. The reasons why remain mysterious. It doesn’t seem like Cahokia was conquered, because archaeologists have found no evidence of battles or large-scale destruction occurring there, although there was a stockade–since reconstructed–suggesting that the city was afraid of some kind of enemy. The causes might have been environmental. As in all dense cities in the medieval world, Cahokia was filthy, and diseases most likely decimated its residents regularly, and almost certainly at a rate that would have caused negative population growth if new residents weren’t moving there from the outside. If the reason why people came to Cahokia in the first place, which we don’t know, went away, the city would begin shrinking. This decline could have been accelerated by a depletion of natural resources. The city’s residents would have needed food and firewood, and after several hundred years of habitation these were probably harder to come by. Climate change may also have played a role, perhaps affecting the corn crops upon which the city’s population depended.

cahokia birdman

Here is a reconstruction of the “Birdman,” perhaps a ruler of some type who was important enough when he died to take 250 people with him to the afterlife.

Whatever the reason, by sometime in the middle to late 14th century, Cahokia was mostly or totally abandoned. The Mississippian peoples began living in smaller, more thinly-spread communities. The houses that were once there decayed away and grass grew in the grand plaza. Eventually all that was left, at least above ground, were the great mounds. Despite the fact that the Mississippians did not have written records, memories and accounts of Cahokia might have survived, if the Native American world was not completely disrupted by a new influence–the coming of Europeans, and most specifically their diseases. In the century after Columbian contact in 1492, perhaps as much as 90% of the indigenous inhabitants of both American continents, North and South, were wiped out by disease. We have no idea what cultural or historical memories perished in that environmental holocaust, but it seems the memory of Cahokia, if it did survive the 15th century, probably died with them.

Cahokia thus remains as one of the greatest mysteries in American history. We don’t know why it was founded. We know little about what went on there or what life was like there. We know nothing about why it disappeared. We don’t know who ruled it or under what system, what language its inhabitants spoke or what gods they worshiped. Even today most Americans have never heard of Cahokia except maybe those who live near the UNESCO World Heritage Site that was declared here in 1982. Yet Cahokia was the largest city in America for centuries. It’s clear there are many things still to learn about this fascinating place, but unless the quiet grassy mounds give up their secrets someday, we may never know them.

The photo of the Cahokia palisade (reconstructed) is by Herb Roe at; the image of the mounds is by Wikimedia user Caroline, both used under Creative Commons 3.0 (Attribution) license. The image of the “Birdman” reconstruction is by former Flickr user jefgodesky and is used under GNU Free Documentation license.