The latest science on the depopulation of the UNESCO World Heritage Site at the Cahokia Mounds, located in the Mississippi River floodplain near St. Louis, leaves the reason for decline of the most populous urban area in what would become the United States a mystery. Cahokia joins the mystery surrounding the demise of the population center at Chaco Culture National Historical Park, another UNESCO site located within the modern boundaries of both the Navajo Nation and the state of New Mexico. One of the ruins at Chaco was up to five stories tall and contained more than 650 rooms.
The urban areas of the pre-Columbian Americas have been as much centers of controversy in modern times as they were centers of population before the colonists showed up. Part of the controversy is the sheer scale of the disappearing populations. The other part is one narrative that justified European claims to the land, terra nullius—“nobody’s land” and therefore free for the taking.
The factual basis for this legal claim to an empty North America was at first supported by science. It was possible to look at the ruins of Chaco and Cahokia and estimate the number of person-hours necessary for the construction. This made the origins of the great cities a mystery, because the image of North American Indians in both legal cases and early academic study was of itinerant hunter-gatherers.
In North America, some cities were depopulated by climate change and some by the swath of disease sown across the entire Southeast by the Hernando de Soto entrada between 1539 and 1542. Empty cities could be taken to mean no civilization, but unlike in Latin America (where only Christian civilization counted), empty cities required explanation.
The building tasks, like the Egyptian pyramids, would require large-scale agriculture producing a reliable surplus. The colonists knew this was so in Egypt because the Bible said so and because Egyptians had farmed the Nile Delta from time immemorial.
It was hard for the settlers to get their heads around the idea that the Mississippi Valley was also farmed from time immemorial. Prior to the 19th century, it was thought that Cahokia and some of the other more prominent ruins were beyond the sophistication of the Indians in the area even if they had been able to grow enough crops to feed the workers.
The most colorful explanation had the mounds built by space aliens, who did their work and went back to from where they came. The last European to peddle this swill was the pseudo-archaeologist and con man, Erich von Däniken, who coined money in a series of books starting with Chariots of the Gods (1969), arguing that all the complex artifacts at North American sites came from space aliens rather than Indians.
The more mundane narrative postulated a lost civilization called for convenience of discussion of the Mound Builders. Without a doubt, there were lots of mounds scattered all around the continent but mostly east of the Mississippi.
The Cherokee people knew about another complex of mounds from about the same time as Cahokia covering over 50 acres of rural Georgia. They are now known as the Etowah Mounds. Some Cherokees hold that our ancestors built them; others say they were present when we migrated into the area. The Etowah Mounds and others like them were much less labor intensive than Cahokia.
It certainly did take a lot of labor to construct what we now know to be not just a major urban district but also one of the largest in the world at the time. Cahokia in 1250 had a greater population than London. It would not be surpassed in North America until Philadelphia grew bigger in the late 18th century.
Monks Mound, the most prominent remaining structure of Cahokia, has about the same sized base as the Great Pyramid of Giza and the circumference is greater than the Temple of the Sun in the Toltec city of Teotihuacán. Other mounds so far discovered in the Cahokia “metro area” number 109.
The city died and the ruins fell silent until European settlers came, invested in the idea that Stone Age Indians could not have built on such a grand scale. The “Mound Builders” remained a lost civilization until the 19th century, when the fact of indigenous builders finally began to take hold.
Cahokia, the greatest of the cities so far discovered in the Mississippi watershed, was abandoned almost 200 years before the Europeans arrived, a timing that exonerates the disease machine that was the DeSoto expedition. The leading theories of what caused the demise of Cahokia are social and environmental, since the decline took place before the predators arrived.
Physical anthropology tells us that Cahokia was just like big cities in modern times in that it was home to a diverse collection of immigrants. The population appears to have risen too quickly to be explained by birthrate only, and the other possibility is immigration, whether by volunteers or by war captives.
A study in the Journal of Archaeological Research examined 133 teeth from 87 people buried at Cahokia to compare the strontium isotope ratios. The strontium isotope ratios in cadaver teeth can be compared to the same figures for small mammals in the area as well as other human populations to determine geographical origins.
One third of all the dead studied at Cahokia were found to be not indigenous to the area, leading some archaeologists to dub the ruins “America’s first melting pot.” This is how cities are, but the assumption seems to be that would not be the case in pre-Columbian times. People certainly did not move by cars, trains, and planes… but, somehow, they moved.
Indians know and archaeologists have slowly proven that people managed to travel before the settlers came. The people at Chaco left things in their trash that showed connections from California abalone shell to copper from the Southeast to parrot feathers from subtropical Mexico.
Cahokia digs have shown the city to be a pre-Columbian Ace Hardware, manufacturing hoes and axes with flint blades. They acquired copper from the Great Lakes, mica from the Carolinas, and shells from the Gulf of Mexico. The river was a superhighway for traders.
From the Spanish conquistadors onward, the invading predators struggled for control of the Mississippi River, considering it the key to trade and therefore political dominance of North America. Few credited the idea that the indigenous people had used the riverine advantage.
In 1803, U.S. President Thomas Jefferson would approve the unauthorized and probably unconstitutional Louisiana Purchase for the very same purpose—control of the trade routes along the Mississippi. Are we to believe the indigenous people never thought of that?
The commercial advantage of the Mississippi explains the location of Cahokia easily and the substantial immigrant population as well. ScienceDaily quoted archaeologists Thomas E. Emerson and Kristin M. Hedman offering an alternative to a common narrative that Cahokia succumbed to flood:
“There is no smoking gun if you want to pin Cahokia’s dissolution on environmental factors. …It makes more sense, given the heterogeneous population with differences in language, and social, religious, and political cultures to look to internal dissension at Cahokia as the underlying reason… Cahokia may be an interesting example of political experiment in the unification of social and ethnic diversity that failed…”
Having become a center of population and commerce by exploiting a location on the river and the upside of diversity, Cahokia was then killed either by the impersonal river or by the downside of diversity. The diverse population simply could not turn the prosperity into tolerance of different peoples who took part in the prosperity.
The U.S. Constitution is a blueprint for very different peoples to live peacefully in the same polity. It is at the root of American exceptionalism that differences in ethnicity, religion, and political opinion did not become centrifugal forces ripping the country apart. The assumption that immigrants brought down Cahokia assumes the ignorant savages could not solve the problem of living with diversity. Like the Six Nations did before the U.S., for example.
Another strong contender for an answer is that the pre-Columbian metropolis was destroyed by a mirror image to the catastrophic drought thought to have ended the urban center at Chaco Canyon. Cahokia is thought to have been flooded. Climate change in the form of localized rainfall set off the flooding of the mighty Mississippi and ended Cahokia. This explanation is hotly contested.
Samuel E. Munoz and his colleagues at the University of Wisconsin and Washington University in St. Louis analyzed sediment cores to date major Mississippi floods over 1,800 years. Reporting in the 2015 Proceedings of the National Academy of Science, the researchers found that there were no large floods between 600 and 1200 C.E., the time when Cahokia was growing in population and influence.
After that time bracket and hundreds of years before the U.S. Army Corps of Engineers would try to tame the Big Muddy, the mega-floods returned and Cahokia was abandoned. The timing of the two events does not, of course, prove that one caused the other.
Munoz reported his findings in May and a rebuttal appeared by July of the same year. Making allowances for the time required to get a paper reviewed, a July reply to an article published in May is instantaneous in academic terms. Sarah E. Baires of Eastern Connecticut State University and her colleagues questioned Munoz’s dates, suggesting that the stratification of the core samples counted back in time from how the land looks now rather than how it looked when Cahokia was abandoned.
Munoz was allowed to respond briefly in the same issue of Proceedings, and he began by disclaiming the idea that floods were the only cause of the Indians deciding to decamp from Cahokia. He maintains flooding was one cause.
Another factor has been in scientific literature for over 20 years: deforestation. In other words, the citizens of Cahokia used up all the wood in the vicinity because they exceeded the sustainable harvest, never figured out how to use the river to move logs, and did not match the ingenuity of the Chaco culture in somehow moving logs over land from the Zuni and the Chuska Mountains to frame the Chacoan pueblos.
This debate purports to be scientific but it cannot escape political context. Baires, continuing the discussion about what we might term the “Noah Theory” of Cahokia’s end, claimed that there are two questions to get past on the way to answering why the Indians moved away:
1. How does settler colonialism affect collapse narratives?
2. How do collapse narratives marginalize indigenous histories?
More is at stake in this debate than ethnic insult offered by conservatives or patronizing by liberals. The framing of indigenous America as populated only by migratory savages took root in the U.S. so deeply that the colonists could not bring themselves to admit the ruins discovered were built by Indians. In the law books, science stood up next to religion to attack Indians’ rights to occupy the soil under their feet.
This framing remains the context of the mystery of Cahokia, the most populous city ever in North America until surpassed by Philadelphia in the 18th century. The very existence of Native American cities threatens the colonial narrative of the state of civilizations in North America.
Iron Age v. Stone Age is a matter of technology, not civilization. Natives already worked softer metals like gold and copper. Bronze and iron would have come in due time had the presence of gold not stirred up colonial predators.
The state of civilization in the Americas before colonization still matters, so it matters whether Indians destroyed Cahokia by overharvesting wood, or the Mississippi River put it under water too many times, or the people of Cahokia could not live with the social diversity that built the city in the first place.
The Mississippian metropolis is long gone, but the mystery of why it fell remains. The only thing for certain is we now understand space aliens did not build it, and no one has yet suggested it was depopulated by alien abduction. Chaco and Cahokia as indigenous accomplishments show that while space aliens did not create them, colonial predators stole them.