A thousand years ago in downstate Illinois, a world-class engineer designed a 100-foot-tall structure that still stands. He made it out of mud.

We’ll never know his name, or the name of the city that was planned and built on a grid system around his squared-off pyramid. His people left no written records. But we know they had to work fast and hard to build it.

Its foundation was 20 feet high, a rectangular platform of gumbo clay roughly 1,000 feet long and 800 feet wide at the base. By itself, the clay would have been worse than no foundation at all–it shrinks and cracks if allowed to dry out. So the engineer found a way to keep it constantly wet. He had buttresses built at the north and south ends, and filled the space between them with another 40 feet of clay and coarser dirt, layered so as to draw water up from below by capillary action. In the Mississippi River floodplain, where the water table was always high, this would keep the clay foundation saturated and solid. For this process to work, the whole thing had to be planned out ahead of time, and the first 60 feet had to go up right away, says soil chemist, geographer, and archaeologist William Woods of Southern Illinois University Edwardsville. “They had to see the end product before they began.”

People in the Mississippi valley had been building smaller, superficially similar structures for 5,000 years, but this was apparently the first and only one to be so carefully engineered. Over the next century or two, people added layers to it, creating the edifice you can see today from Interstate 55 at mile eight. It’s the largest earthwork in the western hemisphere. It was topped by a wood-and-thatch temple and surrounded by four plazas–on the north, south, east, and west–making its city into a mirror of the universe as these people saw it: a circle divided into equal quarters by a cross.

Just as it was more than a pile of dirt, the city surrounding it was more than an agglomeration of villages. Without ever having seen a city, these people invented and built one. Yet today their achievement remains little known. Most Americans grow up knowing more about the people who lived next to the Nile than the ones who lived next to the Mississippi.

Building the structure required 15 million 50-pound baskets of earth–each one dug elsewhere with stone tools, carried on someone’s back to the site, emptied, and tamped into place. In all probability, those who built it had many intertwined motives. They built it for religious reasons–to bring the lower world (earth, water, death) together with the upper world (sky, fire, life). They built it for political reasons–to curry favor with their leader, who was probably known as the Brother of the Sun. And they built it for social reasons–to honor their own kin and join with others in a worthy task, a task that must have combined elements of cheering the Bulls, going on pilgrimage to Mecca, and witnessing the Incarnation.

Names are a problem, because the ones we use for this place are gross anachronisms. It’s as if people in 3000 AD were to call 21st-century Chicago “Qwertyuiop,” after a group of people who’d lived nearby in 2600.

The ingeniously engineered structure is known today as Monks Mound, after a handful of French Trappists who planted kitchen vegetables and wheat on its terraces between 1809 and 1813. The city itself, now long abandoned, is known as Cahokia, after a subgroup of the Illini Indians who lived nearby in the 1600s and 1700s. The culture of which the city was the fountainhead, and which overspread the southeastern U.S., we call Mississippian. That portion of the city now owned by the state of Illinois to protect it from real estate developers (about three and a half square miles out of five) is called the Cahokia Mounds State Historic Site.

We have to have names, but the names are false. Even the neutral but subtly dismissive word “mounds” has nothing to do with those who lived and built and ruled here. Equally false are the European grasses that make the place look like a park today. The city’s thatched wooden houses had hard-packed clay around them; even the mounds may have been covered with clay rather than prairie grasses.

On a clear day you can see the Saint Louis Arch from the top of Monks Mound. Closer by, the greensward and scattered trees are pleasant and welcoming. But they are nothing like what the Brother of the Sun saw when he lived and ruled from here. Other than a few mounds and the Mississippi bluffs in the distance, everything has changed.

All we know, or can hope to know, about these people comes from a combination of great diligence and dumb luck. Diligence is archaeologists’ stock-in-trade. They sift every spoonful of earth, and they map in 3-D where each scrap of bone, corn, pottery, and shell bead comes from. They even keep track of where the dirt changes color.

Consider, for instance, the story of the “bathtubs,” as told in the recently published Cahokia: The Great Native American Metropolis, written by Biloine Whiting Young and the dean of Cahokia archaeology, Melvin Fowler. About 40 years ago, when an interstate highway exchange was planned half a mile west of Monks Mound, archaeologists working ahead of the bulldozers saw stained patches in the soil. As archaeologist and Cahokia Mounds State Historic Site public relations director William Iseminger says, when you dig a hole and fill it in, the dirt never goes back the same way–it will have a different arrangement and over time takes on a slightly different color. So the stains represented ancient holes in the ground. But these holes obviously hadn’t been dug for house poles or garbage pits. They were oddly shaped, eight feet long and five or six feet deep, one side vertical and the other slanting up diagonally. They looked like old-fashioned bathtubs, but what were they really?

The mystery was partly solved when workers at another dig a few miles away found a bald cypress log three feet in diameter in such a hole. The “bathtubs” were post pits, shaped to make it possible to ease huge posts into them. When archaeologist Warren Wittry thought to plot their locations on a map, he saw that they were regularly spaced in a curve, as on an arc of a circle.

It soon became clear that the prehistoric “Cahokians” had indeed designed and put in place a circle of posts. And not just any circle: if you stood at its center on the mornings of the spring and fall equinoxes (usually March 21 and September 21 in our calendar), you would see the sun rise from behind a post and directly out of Monks Mound. Around the winter solstice (December 21), the sun would be seen to rise four posts south, and around the summer solstice (June 21), four posts north. (Over time, at least five different woodhenges were built at this location.) All this from a handful of funny-colored patches of dirt.

Luck happens to archaeologists too. It happened to Thomas Emerson, now an adjunct professor of anthropology at the University of Illinois at Urbana-Champaign and director of the Illinois Transportation Archaeological Research Program. In the fall of 1979, working in a field three miles east of Monks Mound (now covered by the interchange of I-255, I-55, and I-70), he saw an earthmover strike what looked like an old brick. It turned out to be an intricate work of art from the deep past, now known as the “Birger figure.” A woman in a short wraparound skirt is wielding a short-handled Mississippian stone hoe. She’s chopping what looks like earth but is also the back of a snake. The snake has the head of a cat and a tail that turns into a squash vine climbing up the woman’s back.

It’s also lucky for us that Mississippian culture survived Cahokia’s decline and abandonment around 1300 and was still around in 1539, when Hernando de Soto tried to conquer what is now the southeastern U.S. He did battle with chiefs who presided over good-sized towns from atop mounds not unlike Cahokia’s, all described in the chronicles of the expedition. The Mississippians defeated the Spanish, accomplishing what neither Incas nor Aztecs had been able to do. One tribe, the Natchez, lasted long enough as a group for French colonists in the early 1700s to record some of their words and customs.

Without these fragmentary historical records, we would have much less reason to suspect, for instance, that the ruler of prehistoric Cahokia had a special relationship with the sun. And we wouldn’t know that the temples built atop Mississippian mounds sometimes contained the bones of elite ancestors, ornaments, animal pelts, weaponry, wooden statues, and a sacred fire. Excavations at Cahokia’s Kunnemann Mound confirm that elite buildings there had formal circular hearths that were regularly cleaned and relined, like those of their cultural counterparts hundreds of years later.

To us, Cahokia may not seem like much of a city. The best estimate is that it had between 10,000 and 20,000 people at its peak, just a fraction of the population of a single Chicago ward. But it was the first place north of Mexico ever to grow that big, and it remained the only one until Benjamin Franklin’s Philadelphia unwittingly passed it up around 1750. When Monks Mound was being built, Cahokia was roughly the same size as London.

Size matters, but it’s not the rarest thing about Cahokia. The city also represents one of the very few occasions that Homo sapiens has independently invented urban living. That’s one reason Cahokia Mounds isn’t just a state historic site. Since 1982 it has also been on the United Nations Educational, Scientific and Cultural Organization’s list of World Heritage Sites, along with the Great Wall of China, the Grand Canyon, and 627 other places.

Two things made Cahokia possible–corn and the Mississippi. Just downstream from where the Illinois and Missouri rivers flow into the great river, its valley broadens out into a flat, fertile, frequently flooded plain, known locally as the “American Bottom.” Nowadays it’s across from Saint Louis, farmers grow horseradish there, and the river is kept out by levees. But a thousand years ago the Mississippi acted like the better-known Nile. Its spring floods renewed American Bottom fields with sediment from upstream, then receded in time for planting. William Woods draws a circle around Monks Mound: “There’s more cultivable alluvium within two and a half miles of Cahokia than anywhere else in the American Bottom. These people walked to work.” Farther away, but still within a relatively short journey, were the diverse plants, animals, and minerals of four different regions–the Ozarks, the Illinois prairies, the eastern woodlands, and the river valley itself.

Corn, first domesticated in Mexico, took millennia to find its way north. It probably arrived in the midwest before 200 BC, but members of what we call the Hopewell culture, already settled agriculturists, chose to grow it only for ceremonial purposes. Not until centuries later did people adopt it as a food crop.

Becoming dependent on corn, we now know, constituted a prehistoric Faustian bargain. On average, corn growers got more food for their labor than they could from earlier grains like goosefoot or knotweed, and corn stored better too. But in any given year they also faced a greater risk that the crop would fail altogether, leaving them to starve that winter. There was another less obvious trade-off in nutrition. People living primarily on corn may not get enough protein. (No one grew beans, a complementary protein, at Cahokia, though wild beans existed and some neighboring peoples were beginning to cultivate them. “In all our excavations,” says William Iseminger, “we only found half of one bean, and we’re not sure of that.”) Toddlers weaned on corn mush suffered high infant mortality. Those who did grow up wore down their teeth on the fragments of grinding stone left in their cornmeal.

When the Hopewell culture faded and someone invented an improved stone hoe, people did turn to corn as a major crop and daily staple. The stage was set for what we call Mississippian culture.

But just because a stage is set doesn’t mean anyone will choose to perform on it. We have physical evidence of how Cahokians designed and built their mounds and plazas. But we don’t understand why they did these things. Motives don’t show up in the dirt. Why did thousands of people leave their egalitarian villages and self-sufficient homesteads for the new city? And once there, what possessed them to wear themselves out carrying 50-pound baskets of dirt and emptying them where they were told?

One theory long popular with archaeologists was that corn made them do it. In this view, corn didn’t just make a stratified urban society possible, by creating a surplus to feed priests or other specialists too busy to grow their own. Corn made such a society necessary, because then the priests would have a reservoir from which to help out those whose crops happened to fail in any given year.

It’s a comfortable theory. It implies that nothing happened very fast in prehistory and that every part of society performed its function in supporting the whole. It suggests that Cahokians were so communal-minded that they could be counted on to do what their environment, or their ritual, or their agricultural base dictated.

This theory has since collided with archaeological evidence. For one thing, it appears that priests didn’t always redistribute their resources to the poor. (Perhaps that finding will loosen Republican purse strings for the study of prehistory.) And at Cahokia, several things did happen suddenly around 1000 AD: people moved to the city in large numbers, they laid the foundation of Monks Mound, and they even started building their houses differently. This was Cahokia’s “big bang”–a sign that some individual or group took some kind of drastic action that made a difference.

“Cahokia could not have been built merely on communal sharing,” contend U. of I. archaeologists Timothy Pauketat and Thomas Emerson in Cahokia: Domination and Ideology in the Mississippian World. “It did not gradually evolve as a self-sufficient community or mercantile center. In its radically and abruptly transformed landscape and in its distinctive craft products, Cahokia was constructed through the appropriated resources from the entire [nearby] region, returning or redistributing itself and its ideology to those who would be dominated.”

“Redistributing its ideology”? They could be talking about the Birger figure. According to Emerson, Cahokia is unique among Mississippian sites in its production of female figurines. Its leaders may have gained their unprecedented power by monopolizing and enhancing an existing fertility cult. They seem to have controlled even the popular game of chunkey, in which players competed to hit a rolling stone with a javelin. “Early on,” says Pauketat, “we find chunkey stones in all the villages. Then about 1050 they show up only in Cahokia.” Meanwhile, outlying settlements were reorganized and resettled. Ten miles east of Cahokia, Pauketat writes, a village of 200 to 300 people “virtually appeared on the landscape at about A.D. 1050 and then disappeared within five or six decades.”

To understand the construction of Monks Mound is to sense an engineering genius just beyond the horizon of our knowledge. To understand Cahokia’s big bang is to sense a political genius, a Lenin or a Lincoln, who acted to impose his will. Young Shaka Zulu did something similar in southern Africa between 1818 and 1828, when he took power and united a patchwork of related clans into a chiefdom. “No big technological change was involved, just new ideas,” says Emerson. There was no economic or environmental or functional inevitability about the brief flowering of the Zulu nation–it didn’t have to happen. The same goes for the prehistoric midwest. “There are probably dozens of stillborn Cahokias out there,” says Emerson. “We just can’t see them.” Writing in the Journal of Archaeological Research, Pauketat denies that chiefdoms or states grow up in order to resolve some preexisting problem, regardless of what they may claim after the fact. “Cahokia was not caused by the environment, population growth, or technological change.”

William Woods has a somewhat different take on why Cahokia happened. The city, he thinks, “was like the cathedrals in [medieval] France. Someone who was already important had a vision in the right place at the right time. People started coming in to see it and didn’t want to leave the city. It was like a messianic cult, a cult of opportunity: ‘Wonderful things can happen, and we all have to contribute.'”

Was Cahokia held together mainly by coercion or consensus? Fear or love? Melvin Fowler, professor emeritus at the University of Wisconsin Milwaukee, inadvertently raised these questions in 1967. In that year he started a dig that uncovered the most spectacular, gruesome, and complex find in Cahokia’s archaeological history. Fowler’s excavation of Mound 72 at Cahokia remains unusual, since few of the surviving mounds have been investigated.

Mound 72 isn’t large as Cahokia mounds go–it’s roughly 6 feet high, 70 feet wide, and 140 feet long. But to a knowledgeable observer like Fowler, it stuck out like a neon billboard in the wilderness. It runs northwest to southeast in a city otherwise almost entirely organized according to the four cardinal directions (some midwestern practices never change). And it lies near the south end of Cahokia’s central north-south axis. Mound 72 looked like it might be a boundary marker. It turned out to be that and more.

Around the time of Cahokia’s big bang, its planners erected a marker post as part of another woodhenge at the far south end of the city. (Woodhenges may well have been used for surveying and city planning as much as for astronomy.) Not long afterward, two of the new city’s leaders were laid to rest in a rectangular mound near the post–the first of three mounds that were eventually incorporated into what we know as Mound 72. One of the men was laid faceup, the other facedown underneath him. Between them was placed a spectacular, opulent layer of 20,000 Gulf of Mexico shell beads arranged in the shape of a falcon. Around the two men lay further evidence of wealth and prestige: more than 700 arrows bound into quivers and tipped with beautifully made, never-used arrowheads; 15 chunkey stones; and six other people, probably relatives or retainers. When the ceremonies were over, their burial mound was topped off with dirt and its outside coated with a four-inch layer of off-white sand and clay, evidently mixed to resist erosion. Fowler speculates that one of the two men buried with the beads was a “sky chief” and the other an “earth chief.” Did they unite the city in death as in life?

At about the same time, several other important people were buried in a second mound 80 feet northwest, along with somewhat less spectacular grave goods and a few dozen other people. Perhaps 50 years later, a third and much stranger set of burials occurred between the first two. First, more than 50 young women between the ages of 18 and 25 were buried together. Then four males, their heads and hands removed and their arms interlocked, were buried. Conceivably they represented the four quarters of Cahokia and of the universe. All we can say for sure is what Fowler writes in his newly published report, The Mound 72 Area: Dedicated and Sacred Space in Early Cahokia: “All of these individuals were dedicated to, and indicate the great significance of, Mound 72.”

A different kind of death–most likely an execution–came to the Mound 72 area around 1100. Thirty-nine men and women stood on the edge of a pit just southwest of the previous burials. Each was struck with a heavy weapon in the back of the head or neck and fell into the pit. Three were decapitated. They were buried as they fell, several while they were still alive–their fingers had dug into the sand that lined the bottom of the pit. Above this jumble of sprawled bodies were at least two layers of what may have been matting, then 15 apparently honored dead, whose bodies had been temporarily stored elsewhere. After this burial, all the smaller mounds were covered and shaped into the single one we call Mound 72.

Some of the more than 272 dead in this mound–such as those buried with the sky and earth chiefs–were probably willing sacrifices. We can even make a plausible guess as to what they were thinking. When Natchez war chief Tattooed-Serpent died in 1725, at least ten close relatives, servants, and companions sacrificed themselves at his funeral. Some of the French tried to talk one of his wives out of doing so, and she told them not to grieve for her. “We will be friends for a much longer time in the country of the spirits than in this, because one does not die there again. It is always fine weather, one is never hungry, because nothing is wanting to live better than in this country. Men do not make war there anymore, because they make only one nation.”

It’s hard to see the later executions in this gentle light. “These…victims demonstrate that reckoning with Cahokian patrons sometimes had deadly consequences,” argues Pauketat in Cahokia: Domination and Ideology in the Mississippian World. In his view, the Cahokia chiefs had to contend with some degree of resistance. As in other political standoffs, chances are some opponents could be persuaded to go along and others could be bought off or denied rewards. People’s allegiance could be cemented by communal feasts and games and cooperative labors, such as the frequent additions to the mounds and the rebuilding of the woodhenges. But sometimes the chiefs may have killed a few die-hard dissidents (heretics? criminals?) in order to maintain their authority.

However we see the mysteries of Mound 72, Cahokia was neither a democracy nor an egalitarian paradise. William Woods describes the rank-and-file Cahokian’s diet: “What’s for breakfast? Gruel. What’s for lunch? Gruel. What’s for supper? Gruel and a little fish. You might eat venison sometime in your life.” In elite precincts, by contrast, garbage pits reveal big fish and choice cuts of venison.

Cahokia was part of a long-distance trading network extending from upper Michigan to the gulf coast, and from the Smoky Mountains to the Ozarks. (A similar continent-wide network had existed before, in Hopewellian times.) But the city doesn’t seem to have depended on long-distance trade for essential items like corn and wood. Nor did the Cahokia chiefs rule over any people who lived more than a few miles away.

Just as Cahokia wasn’t an empire, it wasn’t a colony. It’s hard to believe that it had no contact with the contemporary Toltec civilization in Mexico, but in more than 100 years of both treasure hunting and scientific archaeology, no one has ever found so much as a bead that can be traced to Mexico. Cahokia rose and fell on its own.

Yet the misconception that there was some connection is durable. In her 1992 popular history of corn, Betty Fussell piled error upon error when she wrote that Cahokia was “built from Maya blueprints.” Could it be that this mistake persists because it’s convenient? Would non-Native Americans feel less guilty about having appropriated Indians’ land if they’d been unable to build a city using their own blueprint?

Cahokia’s golden age lasted no more than 150 years, though for much of this time its population probably hovered between 5,000 and 7,000 people (its peak was 10,000 to 20,000). Around 1150 AD, a new and possibly more sinister construction project began–a solid two-mile-long palisade of vertical logs around “downtown” Cahokia that enclosed 200 acres and 18 mounds, including Monks Mound and the grand plaza. The palisade passed through some house sites, but William Iseminger says it’s impossible to tell if it was built in haste or a few decades after they’d last been occupied. Like most Cahokia constructions, it was rebuilt at least four times.

The palisade is a puzzle. It includes bastions a bit like those found on medieval European castles from which archers could shoot while remaining safe from enemy fire. Yet there’s not much evidence of large-scale warfare at Cahokia itself. Did they put up such a big fence just to make central Cahokia a more secure and exclusive gated community?

Cahokia’s very success may have been its downfall, a downfall that was just starting to become evident when the first palisade went up. William Woods suspects that the Cahokians cut down too many trees upstream in the watershed of Cahokia Creek and on the river bluffs. No surprise there. Every house, temple, and sweat lodge in the area was made from wood and heated with wood, and the woodhenges and palisades were also made of wood. Deforestation meant that Cahokians had to go ever farther afield for fuel and building materials, but it also created a less obvious environmental double whammy. The more a watershed loses its trees, the faster it sheds both soil and water. So when it rains, the soil washes into the stream channel at the same time that the channel has to carry more water. Floods rise faster and higher, eventually inundating fields that were once safe throughout the growing season. Over time such floods from tributaries–unlike the benign Mississippi floods–could well have posed problems for Cahokia agriculture. “They were in a trap,” says Woods. “The agricultural basis for life at Cahokia was literally being smothered.” Around this time the climate gradually began to cool, which may have cut corn yields as well.

“That’s not an explanation,” Emerson retorts. “People are very adaptive.” Flooded fields or a shortage of trees would have presented a management problem, Pauketat explains, yet they wouldn’t have forced people to leave. Still, crop failures could well have undermined Cahokia’s political stability. A priest-lord with no riches to overawe the public or his fellow aristocrats might be vulnerable to an ambitious subordinate.

For whatever reason, burials at about this time suggest that the chiefs’ spiritual authority was indeed declining. At Cahokia’s height, says Pauketat, the supernatural powers “were mediated by the chiefs”–that is, they represented Cahokians to the gods and the gods to Cahokians. Religion was not do-it-yourself. “Then as things became more decentralized, everybody does their own mediating,” he says. “Everyone makes pots that end up in graves. The elite no longer control the distribution of symbols”–as they seem to have done in Mound 72, for instance.

The last part of Monks Mound to be built–perhaps around 1200–wasn’t the top but the lower, south-facing platform overlooking the grand plaza. Woods speculates that it was built to counteract a loss of faith: the priests brought their world-renewing rituals down from the enclosed temple atop the mound and made them more visible in order to reassure a restive populace. “The acoustics are excellent,” he says. “From the grand plaza you can hear people talking up there, if there’s no wind or truck traffic.”

Another kind of catastrophe could conceivably have disillusioned the Cahokian faithful even more. Woods notes that a severe New Madrid-level earthquake hit the area around 1300, give or take a hundred years. This is close to the time that a portion of Monks Mound slid downhill, carrying with it the west wall of the temple. If invaders didn’t defile the sacred mound, perhaps the lower world did.

Just as city life was becoming less compelling, an alternative began to open up in the form of new food sources. Robert Hall, professor emeritus of anthropology at UIC, calls this the “shmoo effect,” after the ubiquitous and tasty animals in the old Li’l Abner cartoon. “Any combination of increased availability or use of beans, bison, or better-adapted corn could easily have spelled disaster for the Mississippian adaptation in Illinois,” he writes in his contribution to Cahokia and the Hinterlands: Middle Mississippian Cultures of the Midwest. (More recent research suggests that better corn probably wasn’t part of the picture at this time.) “Participation in the Cahokia sphere of relations would have had ever decreasing advantages” after roughly 1200. Now as never before, rank-and-file Cahokians could choose to get away and make a living on their own, far from the priests and tax collectors in the American Bottom.

For those who stayed, the end wasn’t pretty. Woods describes a late settlement from around 1300 that was just west of Monks Mound. “These guys were really under stress with corn evident [as food], but not dominating like before. And they seem to be gathering food only within a short distance from their community huddled in the shadow of Monks Mound, as if they were afraid to venture further. I think this impression is real, and their fear was justified.” This spring, excavations by the Illinois Transportation Archaeological Research Program in East Saint Louis showed that part of that Cahokian suburb was destroyed by fire late in its existence. Other places were also burned around the same time, suggesting that the clans that once unified Cahokia may have fallen out.

Why did Cahokia melt away? We don’t know for sure. But is that even the right question? One reason we care so much is that we have in our heads a stereotypical comic-book picture of human cultural evolution–something like the cartoon in which a fish, a reptile, a monkey, a couple of primitive-looking men, and a guy with a briefcase are lined up single file denoting progress. At Cahokia’s end we think we see that parade stopping before it’s finished, and that bothers us.

“Students over and over come in more than ready to believe this idea,” says Pauketat, “that we’re the most civilized culture and others had a chance to evolve into what we are now. It’s very ethnocentric.” More complicated social arrangements aren’t necessarily progress, and they don’t necessarily last. Nor is today’s American society necessarily more complicated or more sophisticated than the society of “primitive” peoples. In kinship, our culture is simpler than most, with “cousin,” for instance, used to denote all kinds of very different relationships and “aunt” used ambiguously to refer to a mother’s sister, a father’s sister, the wife of a brother of either parent, or even a family friend.

Nothing happens automatically in history or in prehistory either. Hopewellians could have grown corn for food and chose not to. Chiefs may lose their grip, or tighten it, in the face of multiple problems. Rank-and-file Cahokians at some point chose to light out for the territory. Timothy Pauketat reminds us that without stabilizing bureaucracies to keep things going, chiefdoms rarely last a long time. Cahokia, he writes, “did not have to happen, and it did not have to last for as long as it did.” If anything, the city’s persistence for two centuries or so, not its end, may require explanation.

Mississippian culture went on long after the Cahokians themselves dispersed. Its people favored fertile river valleys, where they built towns smaller than Cahokia, among them Moundville (in Alabama) and Etowah (in Georgia). Where the Cahokians themselves went is not known. Certain Siouan tribes may have incorporated them, but so much has changed that the evidence is scant.

When Europeans began settling the southeast and midwest, their diseases had already killed roughly four out of every five Native Americans. The survivors were often disorganized and demoralized. Their land looked empty, and the thousands of mounds their ancestors had built were often mistaken for natural hills. (As late as 1916, a prominent Illinois geologist still claimed that they were just hills.) Mounds that were obviously human made were attributed to an unknown “race” called Mound Builders, on the assumption that no Indians could possibly have built anything that grand. Poet William Cullen Bryant visited frontier Illinois in the 1830s and read his people’s own fears back into an imaginary prehistoric war: “The red man came– / The roaming hunter tribes, warlike and fierce, / And the mound-builders vanished from the earth.”

Regardless of where they thought the mounds came from, European-Americans had few compunctions about destroying them. Saint Louis, once nicknamed “Mound City,” obliterated every mound in its path as it grew. Smaller mounds in rural areas were routinely plowed up or torn down for fill to support railroad embankments and, later, highways.

Those who took an interest in the prehistoric past treated it no better at first. They looted the mounds for trinkets. But such relics convey little or no information if you don’t know what layer of soil they came from and which other artifacts they were associated with. Once that information is gone–like the faint soil stains that revealed the extent of the first woodhenge–it’s as irretrievable as the passenger pigeon. And its absence may not even be noticed in a society founded on a falsehood. “Europeans cut down both the people and the trees,” writes historian Kevin Reilly, “leveled the earthenwork ceremonial mounds that had testified to Native American cultural creativity and societal complexity, and called their desecrated graveyard a virgin land.”

Monks Mound itself was too large to tear down. Over time it became overgrown with trees. Visitors from the 1904 Saint Louis World’s Fair plucked off so many branches that the trees died. When the Ramey family sold the first 144 acres of mound area to the state for Cahokia Mounds State Park in 1925, Monks Mound was becoming wooded again. Locals would picnic nearby, and children would race up and down its sides. Later the trees were removed, and when portions of the venerable mound slumped in 1984, many people mistakenly blamed it on the tree cutting. But the popular notion that the trees belonged there is baseless. The Cahokians had no trees on the mounds, and Mound 72 had a special coating. If being treeless could hurt the mounds, they would have washed away centuries ago.

A likely explanation for Monks Mound’s slump, says Woods, is an eventuality no Cahokian engineer could possibly have foreseen. Industries in the American Bottom drew down the water table in the 1940s, ’50s, and ’60s, causing local wells to go dry–and allowing the mound’s clay foundation to dry out and shrink and crack for the first time in nine centuries. When the factories closed or found other water sources, the water table rose again. But the rewetted clay inside the mound couldn’t expand into space now occupied by other soil. The mound’s internal drainage system became clogged, and waterlogged portions started to peel away. Five new drains of thin perforated pipe were recently installed in hopes of controlling the problem.

Meanwhile, U.S. Route 40 had been built just south of Monks Mound, and I-55 and I-70 just north. Across Route 40, a drive-in theater and a 60-home subdivision occupied part of the former grand plaza. Both have since been bought and demolished by the state; the highway, now Collinsville Road, remains. In 1989 the Illinois Historic Preservation Agency erected a superb new interpretive center now visited by 350,000 people a year.

But the forgetting of Mississippian culture takes a long time to undo. “People who could locate Petra on a map of Jordan gave me a blank look when I asked if they knew of Cahokia,” writes Biloine Whiting Young in Cahokia: The Great Native American Metropolis. In the popular mind, “Indian” still calls up images of far western plains warriors, not a city on a grid plan trading over thousands of miles.

Cahokians can be an inconvenient people to remember. They violate the old Indian stereotype by not being savages, and they violate the new Native American stereotype by not being saints. They weren’t environmentalists. They weren’t egalitarian. They weren’t democrats. They didn’t all agree. Their religious beliefs were profoundly dualistic, not monotheistic or New Age. Like Catholics during the Inquisition and Puritans in witch-obsessed 17th-century Massachusetts, they apparently didn’t shrink from killing when their religious beliefs called for it. Like contemporary Americans, they apparently didn’t shrink from capital punishment when they thought it was needed to maintain public order. The city they built failed to sustain itself. Its people lost faith in their leaders and scattered. It returned to the prairie from which it came, and very nearly vanished from human memory as well. Perhaps it would be easier to look away.

For more on Collinsville see the Visitor’s Guide on page 34.

Art accompanying story in printed newspaper (not available in this archive): photos/Jon Randolph.