Did Corn Fuel Cahokia’s Rise?

Today, much of the corn (Zea mays) grown in North America is used to produce corn ethanol – a blend that is added to fuels, primarily gasoline.

But approximately 1,000 years ago, in what is now southern Illinois, corn may have played a pivotal role in fueling the rise of a Native American metropolis. A new study suggests that corn was the staple subsistence crop that allowed the pre-Columbian city of Cahokia to rise to prominence and flourish for nearly 300 years.

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“A social change was taking place at Cahokia and corn basically helped fuel it,” said Thomas Emerson, an emeritus professor of Anthropology at the University of Illinois who led the study. The study findings were recently published in the journal American Antiquity.

Cahokia was the largest city in pre-Columbian North America. It was built by Native Americans known as the Mississippians, who were responsible for erecting some of the most impressive earthen mounds on the continent. At its height, the city boasted several large, flat-topped platform mounds – including the 30meter tall, four-terraced Monk’s Mound, which covered approximately 6 hectares at its base.

It was the city’s focal point and the largest earthen pyramid north of Mexico. Around A.D. 1050, Cahokia rose to dominate that region of the American Midwest where the Mississippi, Missouri, and Illinois rivers converge, a fertile floodplain known today as the “American Bottom.”

The city became a residential, political, and ceremonial center – the hub in a series of interconnected urban centers in the Midwest and Southeast tied together by trade and a shared religion and culture. But its power was relatively short-lived. Cahokia abruptly collapsed by A.D. 1350 when the city’s population declined, possibly as the result of a severe drought and social unrest.

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The ruins of the city can be found today east of St. Louis, Missouri, just across the Mississippi River, between the cities of East St. Louis and Collinsville in Illinois. The site’s spectacular mound complex and its impressive design and layout – it is one of UNESCO’s World Heritage sites – have garnered wonder, awe, and conjecture for the last two hundred years.

Early 19th century lawyer and amateur archaeologist Hugh Henry Brackenridge was one of the first to theorize about the vast city of Cahokia and its inhabitants. In an 1813 letter to President Thomas Jefferson, Brackenridge speculated about the size and grandeur of Cahokia, describing it as having a population perhaps “as numerous as that which once animated the borders of the Nile or of the Euphrates, or of Mexico and Peru.”

Emerson and his colleagues follow in a long line of researchers who have probed the site’s archaeological potential in search of answers to the city’s origins. Unlike their predecessors, however, his team has been using the most modern, cutting-edge technologies to delve into the lives of individuals rather than simply evaluate very broad population patterns.

Specifically, Emerson and his team used isotopic analysis of the teeth and bones of over 100 individuals recovered from previous excavations. The goal of this analysis was to understand what the inhabitants of the city were eating and how their diets changed over time. They correlated this information by directly dating the remains of these individuals using AMS radiocarbon dating.

With technologies such as isotopic analysis, Emerson said, “you can look at an individual and determine their place of origin and reconstruct specific aspects of their diet.”

Isotopic analysis is a powerful tool for analyzing diet. Isotopes are different forms of the same element, like carbon-12 and carbon-13. They have the same number of protons but differ in the number of neutrons. Isotopes are ingested in the foods organisms eat, where they are stored in bones, teeth and other tissues.

By measuring the ratios of certain isotopes in tissue samples, researchers can determine, for example, the types of food an animal consumed. For plants, importantly, carbon isotope analysis can distinguish between different categories of plants, called C3 or C4 plants. These categories describe the ways plants extract carbon dioxide from sunlight during photosynthesis.

Most of the plants in the Midwest fall in the C3 category. These types of plants discriminate against carbon-13 during the photosynthesis process, thus producing tissues with lesser amounts of this isotope.

But corn is a C4 plant, explained Mary Simon, an ethnobotanist and co-author on the paper. These plants are adapted to warmer, drier climates and, unlike C3 plants, they take up the isotopes carbon-12 and carbon-13 in roughly equal measure. C4 plants are therefore highly enriched with carbon isotopes and consequently have high carbon ratios.

In the Midwest and the Eastern United States corn is the only significant C4 plant that is a dietary item, Simon said. “By looking at the isotope ratios in the skeletal material,” she continued, “we can tell whether people ate corn based on the amount of [isotope] enrichment we find.”

The isotopic data in conjunction with the radiocarbon dates allowed the researchers to construct a timeline pinpointing when corn became a staple. The first domesticated crops grown were squash, sunflowers, and other seed-bearing plants but around A.D. 900 the results show that the Cahokians began growing and consuming corn. It was a practice that accelerated in size, effort and scope so that by A.D. 1000, corn played a vital role in the society’s subsistence practices.

Corn originated in Mesoamerica between 10,000 and 9,000 years ago and spread north to the American Southwest by 6,000 years ago, Simon said. But it did not reach the American Midwest and east until much later. Its late adoption in these areas was likely a result of the plants having to adapt to a much shorter growing season. In other words, certain genetic changes had to occur before corn could be grown in the higher-latitude, more temperate climate of the Midwest. “As corn migrated north over thousands of years,” Simon said, “it finally adapted itself to the harsher climatic regime [of the Midwest], which has a much shorter growing season and earlier frosts.”

A greater emphasis on corn production and consumption coincided with the construction of the elaborate mounds – nearly 200 have been identified – that began in earnest around A.D. 1050. This culminated, in the next three centuries, in a city that spanned 2,200 acres and contained upwards of between 40,000 and 50,000 inhabitants.

At its height, it rivaled and even surpassed in both size and population many of the medieval cities of Europe, such as London. It included a rectangular-shaped central plaza capable of holding thousands of people that was encircled by earthen mounds, including Monk’s Mound, and a wooden stockade that was perhaps 20 feet tall.

Semi-subterranean thatched-roofed residences surrounded the central plaza. A vast circle of upright wooden posts lay just to the west of Monk’s Mound. Called “Woodhenge” after Stonehenge in England, it most likely served as a solar calendar, marking the annual equinoxes and solstices.

The researchers do not see the ramped-up production of corn and the emergence of Cahokia as a major urban center as a coincidence.

“Prior to A.D. 900 little hamlets exist,” Emerson said, “which are clusters of families – maybe two or three families. But beginning at A.D. 900 villages appear that have over one hundred houses in them. It’s really a rapid event. And by A.D. 1050, these villages have thousands of people. They also begin to build monumental architecture.”

The researchers do not attribute the emergence of Cahokia as a political, religious and urban center directly to the production of corn agriculture. “Of course, corn doesn’t produce complexity,” Emerson cautioned. “You can find examples of complexity without agriculture and agriculture that doesn’t have complexity.” But the researchers nonetheless believe that corn provided the subsistence security that allowed Cahokian society to develop and flourish.

“You can see the potential of corn to be a dominant crop,” Emerson said. “It’s a crop that can be manipulated and expanded easily. It’s storable, it’s full of energy and protein, it’s sweet, it tastes good, and you can grow large volumes of it. It’s a really good crop to get you through the hard times.”

Corn also eliminates what Emerson calls the population barrier. “You can’t get thousands of people fed on seed crops, but with corn you can,” he added.

One way of maximizing the nutritious aspects of corn and extending its storability is through nixtamalization, a word derived from the Aztec Nahuatl language which describes the process of making hominy. It involves soaking corn kernels in an alkaline solution, such as water-diluted limestone, lye, or wood ash. This retards the growth of sprouts while in storage, releases the kernel from its hard to digest outer husk, and allows the body to better absorb niacin – an essential human nutrient.

The evidence for nixtamalization at Cahokia comes in the form of funnel-shaped, tripod-like vessels called “stump-ware.”  These, Emerson suggested, were most likely involved in hominy production. “There are no predecessors of these vessel types,” Emerson said. “And they show up about A.D. 900.”

While large-scale corn production may have fueled the population needed to construct and inhabit Cahokia, the dramatic social and religious changes that took place between A.D. 900 and 1000 are still little understood.

“We still have the chicken before the egg question with which we’ve had for decades, which is the relationship between this onset of maize agriculture and social complexity,” said Margaret Scarry, an ethnobotanist and professor of archaeology at the University of North Carolina at Chapel Hill, who was not involved in the research.

This is something Emerson acknowledged. “Corn agriculture doesn’t tell you that you should lay out a massive plaza and start building huge mounds all over the place,” he said. “The mystery about Cahokia is what happened socially and culturally at A.D. 900.”

Indeed, explaining the “hows” and “whys” of this Cahokian efflorescence remain elusive. But archaeologists have nonetheless documented and described many of its aspects. These include artifacts unearthed over decades of excavation – objects such as pottery, stone figurines, copper plaques, ceremonial frog pipes, and various other ritual and utilitarian pieces.

Many of these reflect unified religious themes that researchers recognize as distinctly Mississippian. These themes depict images of water, the sky, serpents, birds, and fertility, many of which seem to be associated with the underworld, Emerson said.

These religious themes, it is believed, may have had their origin in fertility and harvest ceremonialism – practices and rituals that have deep time depth but also may have modern predecessors. The ethnographically studied Green Corn Ceremony, which is still celebrated by some Native American tribes today, may have had its origin during these times. But these – and similar hypotheses – remain speculative.

Despite all that has been learned, there are numerous mysteries about Cahokia still to unravel. In many ways, it remains an ancient city shrouded in secrets. But, as this research demonstrates, many of these secrets are beginning to fall as new and innovative technologies – like carbon isotope analyses – are brought to bear on complex archaeological questions. Importantly, these technologies are giving researchers insights into the everyday lives of ancient peoples – insights that would have been inconceivable just a few decades ago.

“This kind of research humanizes archaeology,” Emerson said. “We’re looking at the diets of real people. There’s no longer this nameless mass of ‘Indians’ out there that we’re studying or Mississippian culture. These are people; they have their individual histories and we actually now have the ability to focus in on those histories and understand them.”

Written by Tom Garlinghouse, Ph.D.

Follow on Twitter @GarlinghouseTom

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Tom Garlinghouse
Tom Garlinghouse
Tom Garlinghouse is a science journalist based in Santa Cruz, California.

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