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For almost 25 years I drove past highway signs on I-55 announcing the turnoff for the Cahokia Mounds historic site when – ever I made the trip from Chicago to my childhood home in the Ozarks. I would hesitate, remember the five hours of driving still ahead, promise I would stop next time, and then drive on. After all, I had visited Indian mounds from Wisconsin to Kentucky. How different could Cahokia be? Little did I know that I was passing the site of the first North Ameri – can city.

From AD 800 to 1400, the site now known as Cahokia Mounds, in Collinsville, Ill., about eight miles east of down – town St. Louis, was the dominant city of the Mississippian culture, the most sophisticated prehistoric culture in the Americas north of Mexico. At its height, around 1150, Cahokia had an estimated population of 20,000 people, larger than London at that time.

The same advantages that led European settlers 500 years later to build St. Louis made the growth of Cahokia possible. The convergence of three rivers—the Mississippi, Missouri and Illinois—created a rich flood plain with good soil for farming and a wealth of hunting and fishing. The network of smaller waterways that fed into these rivers made travel easy, and three sur – rounding ecosystems—the Ozark Mountains, the Prairie and the Eastern Woodlands— provided many raw materials.

The Cahokian economy was based on maize, a high-yield crop made even more productive with the introduction of hoe cultivation; specialized flint hoes were distinctive to Mississippian culture. Higher yields from the land led to population increases. Towns began to form and expand, bringing more social complexity and centralized authority.

With a stable food supply, the Mississippians of Cahokia were able to support skilled craftsmen and an increased trade for materials and goods. Artifacts found at the site display fine craftsmanship: tens of thousands of shell beads, flint clay statuettes in human and animal forms, dramatic effigy bottles and bowls, and engraved copper plates. Artists had access to exotic materials traded over considerable distances: copper from the upper Great Lakes, mica from southern Appalachia and seashells from the Gulf of Mexico.

The remains of Cahokia, named after an Indian tribe who lived in the area in the 1600s, cover 3,300 acres in the flood plain known as the American Bottom. A 40-acre rectangular plaza, artificially leveled and filled, served as both marketplace and ceremonial center for the city. Flat-topped mounds were built around the plaza, which was surrounded by a two-milelong log stockade. Apparently built for defense, the stockade also was the architectural representation of a hierarchical society. The temple and homes of the elite were segregated inside the stockade, while smaller plazas and residences were clustered outside.

Cahokia was surrounded by outerlying communities that made up the “greater Cahokia area.” The remains of 120 mounds are there, more than at any other Mississippian site, made of tamped earth dug out of holes known as borrow pits. Because the Mississippians had no pack animals, laborers carried the earth in baskets on their backs, 50 to 60 pounds at a time.

Monks Mound is the largest of the flat-topped mounds at Cahokia. Named after French Trappist monks who gardened on the mound in the early 1800s, it stands at the north end of the central plaza and covers 14 acres. Archaeologists estimate that Monks Mound alone took 15 million baskets of earth to build.

The more unusual conical and ridge-topped mounds were used for burials and to mark important locations. Excavations have centered on Mound 72, which accommodated almost 300 burials. The most dramatic of these was the ceremonial burial of a man in his mid-40s who is believed to have been an early leader of Cahokia. He was laid out on a platform of 20,000 marine shell beads, arranged in the shape of a falcon—an image that appears frequently on pottery and ritual objects found in Mississippian sites.

The remains at Cahokia also include five large circles of evenly spaced red cedar posts, each surrounding a central post. These “woodhenges” appear to have been sun calendars: Certain posts align with the rising sun at the equinoxes and solstices when viewed from the center. Woodhenges may also have served as surveyor’s instruments, used to properly place new ceremonial plazas and mounds within the city. (The Illinois Historic Preservation Agency has recon struct ed a woodhenge on site, and holds public sunrise services to celebrate the equinox and solstice.)

Cahokia began to decline in about 1250, shrinking in both population and area; by 1400 the city had been abandoned. Excavations show no sign of epidemic, invasion or natural disaster that would account for the city’s demise. Paradoxically, scholars believe that the maize-based economy that was the foundation of Cahokia’s success was the eventual cause of its failure. Maize was more productive than native cultivated plants, but it was also more sensitive to changes in weather conditions. Moreover, yield increases led to increased populations that were difficult to support in times of crop failure. Weather patterns began to change around 1200, bringing cooler, drier summers, shorter growing seasons and local food shortages.

In the years of Cahokia’s decline, some of the settlements moved away from the flood plain to higher ground. Carbon isotope studies of human bones from the new sites reveal that maize was supplemented by a renewed reliance on native seeds and nuts. Smaller settlements with a more diversified food base had neither the ability nor the need to support Cahokia’s complex social organization. As archaeologists David Rindos and Sissel Johannessen describe it, “Cahokia didn’t collapse, it evaporated.”

The fall of Cahokia did not mean the end of Mississippian culture, however. When Fernando De Soto landed at Tampa Bay in 1539, he found flourishing Mississippian chiefdoms from Florida to the upper Tennessee River valley, with an estimated population of more than 1 million. Slowly decimated over the years by European illnesses, the chiefdoms were finally destroyed in a series of wars with the French between 1716 and 1731, more than 300 years after the fall of Cahokia.

In 1982 Cahokia was named a United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage site for its importance in North American prehistory.


Originally published in the April 2008 issue of American History. To subscribe, click here