Centuries of Secrets at Cahokia Mounds

Cahokia Mounds State Historic Site preserves the history of an advanced pre-Columbian civilization.

Have you heard of Cahokia Mounds State Historic Site? If not, you’re not alone. Despite its status as the most important archaeological site in North America, most people are not familiar with this lost city in Southern Illinois.

It’s suffered a myriad of indignities. For one, it’s named for a tribe that arrived centuries after its original inhabitants disappeared. Another: its crowning achievement, a pyramid even greater than Giza’s, was named for a group that lived nearby for less time than it takes to get a college degree.

A thousand years ago it was the epicenter of civilization, and now a four-lane highway cuts through the middle of it, a highway that is ironically part of why it’s still around.

This is part of our EPIC Southwest USA road trip from the Chicago-area to San Diego and back!

Cahokia Mounds State Historic Site is one of 23 UNESCO World Heritage Sites
Cahokia Mounds State Historic Site is one of 23 UNESCO World Heritage Sites

Cahokia Mounds State Historic Site in Collinsville, Illinois, uniquely illustrates America’s past, both pre-Columbian and post- “discovery.”

The site, one of 23 UNESCO World Heritage Sites in the U.S., preserves the history of a city that existed long before Columbus stumbled onto that Bahamian beach. It tells the tale of those who built it and those who came after, from Trappist monks to a 19th century mechanic to the archaeologists who preserve their stories.

Cahokia Mounds is continuing proof that civilization on this continent did not begin with the arrival of Europeans.

One of the mounds at Cahokia State Historic Site
One of the mounds at Cahokia State Historic Site

History of Cahokia Mounds State Historic Site

At first glance Cahokia Mounds historic site may seem like just a bunch of dirt mounds, but it’s much more than that. This planned city covered six square miles dotted with 120 earthworks, and seventy of them remain on the site’s 2200 acres.

The community began around 700AD, about the time the Chinese invented gunpowder, as a cluster of small settlements. Over the next couple of centuries those merged to become a larger community.

Interpretive sign at Cahokia Mounds State Historic Site
Interpretive sign at Cahokia Mounds State Historic Site

By 1050 – 1150 the population had exploded to anywhere from 20,000 in most estimates to as high as 50,000 in others. To put this in perspective, London’s population was around 20,000 and the Tower of London was constructed during this period.

About a third of the inhabitants of Cahokia were immigrants, making this city North America’s original melting pot.

By 1350 they were gone. Nobody knows where they went, or why they left.

Inside the interpretative center at Cahokia Mounds
Inside the interpretative center at Cahokia Mounds
The interpretive center inside the museum tells the story of the people who built these mounds
The interpretive center inside the museum tells the story of the people who built these mounds

The mounds they built are the only reminder and remainder of their existence. Some were used for religious and ceremonial purposes.

Others were used for more “earthly” reasons. Mound 72 was a burial chamber filled with five mass graves of sacrificial victims, some beheaded and others buried alive, as well as more dignified burials for the nobility.

Archaeologists also found a copper workshop and a large Woodhenge, used to mark time and the changing of the seasons.

Because the inhabitants, like most peoples indigenous to the continent, had no written language, what is known of their culture is due to the investigations of archaeologists skilled in literally unearthing its mysteries. It’s remarkable that they have as much with which to work as they do.

Introduction to Cahokia Mounds IL outside visitor center and interpretive museum
Introduction to Cahokia Mounds IL outside visitor center and interpretive museum

When the French arrived in the early 1600s they found the Cahokia tribe in the area, hence the modern name of the site. These Illini plains Indians had no knowledge of the previous inhabitants, so they couldn’t explain the mysteries or tell them who built Cahokia. 

Similar mounds, found across the Mississippi River, were razed and looted to become the city of St. Louis, and now only one significant mound remains in that area.

You can just see The Gateway Arch in St. Louis in the distance
You can just see The Gateway Arch in St. Louis in the distance

In the early 1800s a group of French Trappist monks planted gardens on one of the terraces of the largest structure at Cahokia. This structure is now known as Monks Mound, even though the monks were only on-site from 1809 to 1813. 

To call it a mound seems to do it a disservice. The base of this beast covers over fourteen acres and the pyramid rises to a height of one hundred feet.

Monks Mound contains twenty-two million cubic feet of earth – larger in volume than the Great Pyramid of Egypt – and every foot of it was carried by hand in baskets. There are four terraces, and at the top of the highest sat a structure that was fifty feet tall.

Now you can see the Gateway Arch in St. Louis from its summit.

View from the top of one of the terraces on Monks Mound
View from the top of one of the terraces on Monks Mound
Stairs leading to the very top of Monks Mound
Stairs leading to the very top of Monks Mound

In 1831 a mechanic by the name of T. Amos Hill (coincidentally) bought the tract containing the mound and built a house at the top.

When Hill built a well he pulled up not just dirt, but also human bones, pottery shards, and other evidence that the hill was man-made.

As you can imagine, the water was not exactly palatable. A Mr. Flagg recounted in a journal in 1838, published as The Far West, that the odd taste was most likely due to the fact that “the precious fluid has probably filtrated, part of it at least, through the contents of a sepulcher.”

Ick.

Monks Mound at Cahokia Mounds
Monks Mound at Cahokia Mounds

In 1864 the tract was purchased by Thomas J. Ramey. For nearly sixty years he and his family lived on the mound, but they also protected the area.

As a member of the Illinois General Assembly, Ramey pushed for its preservation. For years he and others, most notably archaeologist Warren K. Moorehead, tried to get the area designated a park, but it wasn’t until a grassroots campaign in the early 1920s proved Cahokia’s significance that the state legislature passed a bill granting protected status. With 144.4 acres, Cahokia Mounds State Park was born.

One of the striking things about Cahokia is that U.S. 40, or Collinsville Road, runs right through it. Authorized in 1806 by Thomas Jefferson as the National Road, the section through Cahokia wasn’t officially completed until the 1920s, but by that time wagons, trains, and streetcars had all cut through the complex and the route was well established.

Overlooking US 40 cutting through Cahokia Mounds
Overlooking US 40 cutting through Cahokia Mounds

What helped to save this evidence of the Cahokia civilization and those before  them was the Federal Aid Highway Act of 1956. This legislation allowed for some of the money allocated for highway construction to be used in salvage operations for archaeologically significant sites that were in the path of progress.

In 1960, Interstates 55 and 70 were about to go right through Cahokia Mounds. Activists took advantage of those funds and discovered a series of “Woodhenges,” providing increased understanding of the historical significance of this Mississippian culture. 

In 1964, Cahokia Mounds was declared a National Historic Landmark, in 1966 it was added to the National Register of Historic Places, and in 1982 it became one of UNESCO’s World Heritage Sites.

Today this treasure trove of history opens the door to the past. With continued research, study, preservation, and appreciation, its forgotten secrets will be revealed for future generations to remember.

Cahokia Mounds is featured in Two Lane Gems, Vol. 1: Turkeys are Jerks and Other Observations from an American Road Trip

Visiting Cahokia Mounds State Historic Site

Cahokia Mounds State Historic Site is located east of St. Louis, MO, in Collinsville, IL off Interstates 55-70 and 255, and Illinois 111.

  • Address: 30 Ramey Dr, Collinsville, IL 62234
  • Website: cahokiamounds.org
  • Hours: The grounds are open daily from dawn until dusk and the Cahokia Mounds Museum & Interpretive Center is open Wednesday through Sunday from 9 am to 5 pm.
  • Admission: Admission is free, but there’s a suggested donation of $7 for adults, $5 for seniors, $2 for children, and $15 for families.

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