Many Americans are shocked to learn that their country is home to an ancient pyramid that stands as tall as 100 feet. Mysteriously, the fascinating history of Cahokia and its Monks Mound pyramid aren’t covered in most schools. Be that as it may, Cahokia was the largest pre-Colombian urban settlement north of the Rio Grande. And at its peak, it even had a bigger population than London at the time.

Cahokia started developing in the 10th century, and it became the most important settlement to the Mississippian culture from around the year 1050. Over the course of a couple centuries, Cahokia’s population would grow to as large as 40,000 people. And throughout their city, which took up an area of around 6 square miles (16 km2), the Cahokians built hundreds of mounds.

While the Cahokians left behind no written records, we know that the city was a thriving center of trade. It’s located just outside of modern-day St. Louis, while various materials found at the site come from as far as the Gulf Coast and the Great Lakes.

But for some reason, by around the year 1400, the city was mysteriously abandoned. There’s still a lot we don’t know about the ancient metropolis, but the city’s layout reveals a highly advanced knowledge of astronomy and geometry.

Today, despite its relative obscurity, getting to the Cahokia mounds is surprisingly easy. The site is a relatively short drive from St. Louis, while a tour around the mounds shouldn’t take more than half a day.

Learn more about transport and accommodation at the end of the article.

Cahokia Monks Mound
Walking up Monks Mound

Who Were the Mississippians?

The Mississippian culture lasted from around 1000 – 1500 AD. And remnants of their cities can be found throughout nearly a dozen states across the eastern half of the US. 

The culture is named as such because it mostly developed around the Mississippi River Valley. But no other settlements come close to the size or importance of Cahokia, located in present-day southwest Illinois.

There are various Mississippian cultures and subgroups, with the culture who built Cahokia being categorized as ‘Middle Mississippian.’ Nevertheless, Cahokia was a relatively diverse metropolis, where people from around North America gathered for work and trade. 

The Mississippians relied heavily on agriculture, with their most important crop being corn. Like Mesoamerican cultures to the south, the Mississippians also placed a heavy emphasis on rain and rain-related deities.

Another thing the Mississippians liked to do was built mounds, though they were hardly innovators of the tradition. In fact, Native Americans had been building mounds for at least 1,000 years before the Mississippians came along. Yet in the past, areas comprising of numerous mounds were mostly used for rites and rituals, but weren’t habituated.

The Mississippians, in contrast, built entire cities around their mounds, with large pyramidal structures playing a vital role in their urban landscape.


Approaching Cahokia from St. Louis, I first encountered one of its most sacred sites about half a mile (850m) west of the ancient city center. The area, now commonly referred to as Woodhenge, consists of a circle of posts which functioned as a viewing center for astronomical phenomenon.

The wooden posts there today, obviously, are recent additions. And according to archaeologists, the post holes were rebuilt as many as five times between 1100 and 1200. The overall size of the circle was enlarged each time, though the posts in place today represent the circle’s third incarnation, which is 410ft in diameter.

Cahokia Woodhenge

In the very center of the circle was another pole, where observers would stand to watch the sunrise on special occasions. For example, every year on the morning of the spring equinox, the sun would rise directly over the lower tier of the Monks Mound pyramid.

Meanwhile, the pole in the circle at 30.8 degrees left of center marked the summer solstice sunrise position. And another pole at the same angle to the right of center marked the winter solstice sunrise position.

Cahokia Woodhenge
A miniature model of Woodhenge at the Cahokia Interpretive Center

Monks Mound

As mentioned above, Cahokia’s central and most prominent pyramid is known as Monks Mound. But, as we’ll go over below, that’s definitely not what the ancient Cahokians would’ve called it!

The largest earthwork in the Americas, Monks Mound covers an area of over 14 acres. And archaeologists estimate that it consists of over 22 million cubic feet of earth. Nobody knows for sure how it was built, but some suspect it was all done by hand, with locals carrying countless baskets of dirt from around the area.

Cahokia Monks Mound

But not all at once. Monks Mound was built in several stages beginning around the year 950. And the final stage was completed around 1200, shortly before the city’s sudden decline. Obviously, such a massive, continuous project likely had a purpose beyond just keeping the townsfolk busy.

But why go so far to build such a big pile of dirt? As we’ll go over below, Monks Mound played a central role in the Mississippian vision of the cosmos.

Cahokia Monks Mound

Before climbing up the pyramid itself, I first encountered a series of wooden posts near the parking lot. The city of Cahokia, in fact, was entirely bordered by a massive wooden wall. According to estimations, the whole thing required up to 20,000 trees! Obviously, the posts here represent just a small example of what the wall probably would’ve looked like.

Not only were there walls around the entire city, but various sections of the mound were walled in as well.

At various intervals along the wall were bastions which likely came in handy for defense. But we don’t how frequently the Cahokians were at war. The walls may have also delineated the sacred space of central Cahokia, which possibly functioned as a living ‘temple city.’ Most likely, the wall served multiple functions at once.

Cahokia Monks Mound
Cahokia Monks Mound

Arriving at the base of the mound, it started to sink in just how monumental the earthwork really is. Enlarged several times throughout its history, the original ramp up the pyramid would’ve been lined on either side with posts. And while we don’t know for sure, it’s probable that only the elite would’ve been allowed access. 

The first tier of Monks Mound is flat and spacious, and evidence suggests that various buildings once stood here. They were likely used by priests for special ceremonies, as it was here that the sun would be seen rising from Woodhenge at each equinox. Interestingly, there’s also a small additional mound built on the southwest corner.

It’s unclear whether or not any of the Cahokian high priests would’ve lived on the mound permanently. But more recently, this level of Monks Mound was indeed home to some permanent inhabitants.

In the 1730’s, French priests built a cabin for themselves on the spot as they preached to nearby Native American tribes. And for this reason, the pyramid as we know it today is called Monks Mound. Archaeological excavations, in fact, wouldn’t even take place in the area until the 20th century.

Cahokia Monks Mound
Cahokia Monks Mound

Walking along the first tier of the pyramid, I ascended the next set of stairs to the top of the mound. Today, the very top is a flat, empty platform with little more than a pathway and a bench. But a thousand years ago once stood Cahokia’s largest building, as big as 104 by 48 feet.

What’s more is that a large post, possibly as high as 40 feet, arose directly from the center of the pyramid’s summit. Given the frequent storms that pass through the area, the central post of Monks Mound would’ve attracted frequent lightning strikes (even today, a sign warns visitors to stay away during storms!).

This would’ve been quite the spectacle for the civilian population watching from down below. As archaeologist William F. Romain points out, bolts of lightning striking the post would’ve symbolized the connection between the earth and heavenly realms, if only for a brief moment.

Standing atop the pyramid, I couldn’t help but recall another spectacular pyramid temple I’d once visited. In the 1050’s, at the same time that the main portion of Monks Mound was being filled in, Angkor’s Baphuon temple was under construction on the other side of the world.  

And while the Baphuon is made of stone, the two pyramids share more in common than just timing. Though no longer visible today, the Baphuon once had a long bronze tower sticking out directly from its top. And what’s more is that while the temple was mostly made of sandstone, its core happened to be a large earthen mound. Furthermore, like Monks Mound, the Baphuon even had a long causeway leading up to its main entrance.

Cahokia Monks Mound

Even to this day, Monks Mound remains the tallest structure in the immediate area by far. And the very top offers excellent views of all the other mounds contained within the vast city.

Today, off in the distance, you can clearly see the modern skyline of St. Louis, Missouri. It seems rather fitting that the North America’s largest earthwork offers a view of the country’s largest public monument!

Cahokia Monks Mound

The main structure which once stood atop of the pyramid was perfectly aligned with true north. Yet Monks Mound itself is slightly off center, at 5 degrees east of true north. Given the Mississippians’ geometrical and mathematical expertise, however, it’s unlikely that this was done in error. But why just 5 degrees off?

Romain points out that Monks Mound, as looked at from the sky, shares the dimensions of what’s known as a Root 2 rectangle. This shape, which can also be found numerous other times throughout Cahokia, is produced as follows: take a square, and then extend its length on two sides so that they equal the length of the original square’s diameter.

Cahokia Monks Mound

By standing in the very center of Monks Mound, which is a Root 2 rectangle tilted 5 degrees off center, one can observe notable astronomical phenomenon in each corner at certain times of the year. One corner is the location of the sunrise on the summer solstice, another is the moon’s maximum south rise, another is the winter solstice sunset, and the last is the maximum north set of the moon. 

If it wasn’t clear enough already, Monks Mound was much more than a pile of dirt!

Cahokia Monks Mound

Like many other cultures around the world, Mississippian cosmology emphasized the concept of the three worlds: the upper, middle (where humans live) and underworld. It’s very likely that Monks Mound, similar to the stone pyramid temples of the Khmers and Teotihuacanos, was seen as a bridge between these three realms situated along a vertical axis.

As mentioned above, the pole at the top helped form a link between our world and the heaves. Meanwhile, as we’ll go over below, the city’s location helped Monks Mound establish a symbolic connection with the underworld. And in many world cultures, the underworld has long been associated with the element of water.

Cahokia Monks Mound

Walking back down from the pyramid, I was ready to explore the rest of the ancient city. But there’s no way to ignore the modern highway that cuts right through it. It’s an eyesore, for sure. But as I’d later learn at the Cahokia Interpretive Center, we should be thankful that any of this has been preserved at all. 

Cahokia Monks Mound

Around the Grand Plaza

Just south of Monks Mound is the area that was once home to the massive Grand Plaza. It was a large square area which took up around 40 acres in total, and to the south it was bordered by the ‘Twin Mounds’ (more below). 

It was here that the Cahokian game of Chunkey was played. Nobody’s completely certain of the rules, but it likely involved one man throwing a wooden javelin at another man’s disc-shaped stone.

The plaza was more than a sports arena, however. And archaeologists believe that the Cahokians deliberately made it as flat as possible, taking dirt from the higher areas and placing it on parts with lower elevation. But why?

Cahokia Grand Plaza Mounds
Cahokia Grand Plaza Mounds

Given the site’s proximity to the Mississippi River and Horseshoe Lake, the entire area would’ve been flooded during rainstorms, taking on the appearance of a large lake. And as strange as it may sound, this flooding would’ve likely been welcomed by local residents.

While flooded, the Grand Plaza would’ve symbolized the watery underworld from Mississippian cosmology. And Monks Mound would’ve appeared as an island emerging out of the water, a scene of great symbolic importance to the Mississippians. As with many other cultures around the world, such as the ancient Egyptians, primordial waters play a central role in many Native American creation myths.

Cahokia Museum
Monk's Mound surrounded by four plazas, with the Grand Plaza to the south being the largest by far

As we went over, Monks Mound likely represented the bridge between the sky, the underworld and our earthly realm. But in regards to the horizontal axis, Mississippians believed that the middle realm of humans was divided into four quadrants. 

And the Cahokians likely perceived Monks Mound to be right in the center of this world. While the Grand Plaza is by far the largest section of the city, recent LIDAR laser technology has revealed three additional plazas on the other sides of the pyramid. 

Though we have no former residents to ask, these plazas likely represented the ‘four corners of the world.’ Such imagery repeats itself again and again throughout world cultures, represented in everything from Mesoamerican codexes to Tibetan mandalas.

I continued walking south through the spacious grassy plane. And occasionally, I’d come across other mounds scattered about here and there. According to anthropologist Tim Pauketat, many of these mounds had sweat lodges on top where important healing and cleansing rituals likely took place.

Cahokia Grand Plaza Mounds

Some, but not all, of the mounds were used for burials – most likely for the Cahokian elite. One such possible example is the Twin Mounds at the southern end of the main plaza. Excavations into the mounds have yet to take place, however.

And nearby the Twin Mounds, I encountered a peaceful walking trail pretty much completely devoid of other visitors. Heading east, I came across another replica of the ancient border wall which would’ve surrounded the entire city.

Cahokia Grand Plaza Mounds
Cahokia Grand Plaza Mounds

The ‘Southern Stockade’ represents one of the numerous bastions that would’ve been used for defense. And archaeologists have found evidence of four different walls built in this one area. Given Cahokia’s long lifespan as a major city, it’s not surprising that they’d fix up the walls several times over the years.

Cahokia Grand Plaza Mounds
Mound 55
Mound 50

Cahokia once had over 200 mounds, only around half of which are clearly visible today. Heading back north in the direction of Monks Mound, slightly east of the Grand Plaza, I came across some mounds numbered in the 50’s.

Mound 55 was once a rather important site. There’s evidence that a building stood at the spot before the mound was constructed. And after its completion, a newer structure was added on top. At one point, this significant mound may have even stood as high as 30 feet, offering clear views of the Grand Plaza to the west.

Mound 50, meanwhile, dates back to the 1200’s. Though much of it was destroyed, archaeologists actually rebuilt it to return it to its former size. Like Mound 55, a structure once stood at the spot before the mound was built. As you can probably tell, nearly every mound around Cahokia has its own little backstory.

The Cahokia Interpretive Center

No visit to Cahokia is complete without stopping at the Cahokia Interpretive Center. Around the museum, you’ll get the chance to learn more about Cahokia’s history, Mississippian culture, and the fight to save Monks Mound in the 20th century.

The Bird Man

Cahokia Museum Bird Man

One of the most peculiar things about Cahokia is that despite being the largest city in the region for so many years, hardly any artwork has been found there. One exception is the ‘Bird Man Tablet’ found at Monks Mound itself. But in contrast to the gargantuan pyramid, this sandstone tablet could easily fit in your pocket.

The tablet dates back to 1300, well after Cahokia’s peak. Be that as it may, the carving has since become the de facto symbol of Cahokia itself.

Avian imagery has been discovered at numerous sites linked with the Mississippian world. Many depictions of the Bird Man were carved of copper. But strangely enough, despite no copper artwork having yet been discovered at Cahokia, a copper workshop was found near Mound 34, east of Monks Mound.

But what does the Bird Man represent? We can surmise that he represented the upper realms and man’s link with the heavens. And he likely played a similar symbolic role to that of Quetzalcoatl in Mesoamerica, Garuda in India, Horus in Egypt or the Phoenix in China.

Cahokia Museum

Around the museum, you can find a few of the other effigies discovered around Cahokia, as well as examples of some of the stone tools the people worked with. One exhibition described ancient burial practices, while a large portion of the center is dedicated to Cahokian architecture.

So little is really known about how the Mississippians dressed or what their buildings looked like, however. The depiction of the local residents and their thatched-roof huts at the museum, then, is as good a guess as any.

Cahokia Museum
Cahokia Museum

St. Louis, just across the river, was also once home to many mounds as well. In fact, it was even once nicknamed ‘Mound City.’ But sadly, most of those mounds were gradually destroyed and paved over throughout the 1800’s.

Either mounds were destroyed for simply being ‘in the way,’ or their soil was taken by local farmers who deemed them of no particular importance. And Cahokia could’ve even suffered the same fate had people not lobbied for its protection and preservation.

Even into the early 20th century, there were those who argued that Monks Mound was a completely natural formation. There’s no way that primitive peoples could build such a monumental earthwork, many believed. This attitude only changed in the 1920’s, after archaeological excavations revealed ancient artifacts and even ritual burials.

Thankfully, the site remains well protected today (even if a road runs right through it) and it’s been designated as a UNESCO World Heritage Site. But the question still remains: why have so few people heard of Cahokia, the most significant archaeological site in the United States? 

Hopefully, one day that will change. But at least for now, it’s still fun to show people pictures of Monks Mound, watching their reaction as you tell them there’s a huge pyramid in Illinois, of all places.

See all US archaeology articles here

Additional Info

From St. Louis, first take I-55/70, 64 or Highway 40 & 44 to get to the Poplar St. Bridge. Go over the Mississippi River into Illinois and follow I-55/70 to Exit 6. Turn right onto Highway 111 South. At Collinsville Rd., make a left.

Collinsville Rd. is where you’ll find both Woodhenge and Monks Mound, while the Interpretive Center is about 1.5 miles south.

Cahokia is free to visit. The Interpretive Center is free as well, though on their web site they suggest a donation of $7.

With the exception of major holidays, the Interpretive Center is open Wednesday through Sunday from 9:00 – 17:00.

Tip: Eat something in St. Louis before your departure. The town near the mounds has few options besides a Waffle House, and it’s not the type of area you want to stick around in.

If you don’t have your own rental car, taking a taxi from St. Louis is another option. Just be aware that there’s also a town called Cahokia around 10 miles away. The Cahokia Mounds are located in Collinsville, not Cahokia.

Before visiting St. Louis, understand that public transportation is virtually nonexistent. And while not a huge city, it’s much too spread out to walk comfortably from place to place. Unless you’re willing to ride an Uber every day, having a car is a must. With that being said, staying somewhere relatively central is a good idea. Some of the highest-rated hotels in the city center include Drury Plaza St. Louis at the Arch and The Last Hotel. You’ll also find plenty of Airbnb options as well.

Cahokia plays a major role in the recent book called America Before: The Key to Earth’s Lost Civilization by Graham Hancock. My visit to Cahokia took place before the release of the book, and while I have yet to read the whole thing, Hancock provides a lot of excellent insight into the ancient city.

In his book, Hancock also cites the research by William F. Romain mentioned above, which you can check out here.

At Cahokia itself, there are also a number of informative books available at the Interpretive Center gift shop.

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