For history lovers, you won’t find a better place than the Cahokia Mounds in Collinsville. Many Illinois residents may be surprised to learn that this incredible historic site exists right in their own backyard. After all, it’s not every day that you get to visit a UNESCO World Heritage Site. You'll want to put on your most comfortable walking shoes for this journey.

The Cahokia Mounds are the remains of what was once a thriving ancient city.

While there’s still a bit of a debate on when the area was occupied (and by whom) it’s believed that the area we see now with the mounds was settled around 600 C.E. and the building of the mounds began around the 9th century.

The inhabitants who lived in this city left no written records of their everyday lives, so historians and archaeologists have had to piece together the puzzle through artifacts and other materials that have been unearthed.

Symbols on pottery and stone have helped, but mysteries remain. For one thing, the city’s original name is unknown. The mounds were named after the Cahokia tribe, a tribe that was living nearby when the French arrived in the 17th century, but by that time the mounds had been abandoned by the original inhabitants.

The 2,200-acre park contains about 80 human-made mounds, but the original city was much larger.

Originally, there were roughly 120 mounds of various shapes and sizes. Each one was made by hand, one basket of dirt and clay at a time, which took several decades. It’s the largest prehistoric earthworks construction in the United States. During excavation efforts, it was revealed that these mounds each had different purposes. Some were residential, some were ceremonial, and some were reserved for other things.

For example, about 250 skeletons were discovered in Mound 72.

It’s believed that most of these skeletons were sacrificial, but there are a few that have had historians furrowing their brows. Four young males missing their hands and heads remain a mystery, as well as what looks to be a mass burial of 40 men and women who appear to have been violently killed, or possibly even buried alive. But why? We may never know.

The largest mound is Monks Mound.

It was the crown jewel of the city. Clocking in at 10 stories tall (100 feet high) and covering 13.8 acres, it’s the largest man-made earthen mound north of Mexico. This massive mound was built over the course of several centuries, and archaeologists believe that there were as many as 10 different construction efforts.

Archaeologists have discovered that this massive city even had walls.

And it potentially had a population upwards of 40,000 people at its peak. That’s a lot of mouths to feed, and that ended up becoming a potential factor in the downfall of this once-thriving city. Polluted waterways and difficulties keeping a steady supply of food were some of the main reasons the city was abandoned around 1350.

One of the most fascinating finds is the Cahokia Woodhenge.

A series of large wooden circles were found, and it’s believed that this was a type of solar calendar, capable of marking equinox and solstice sunrises and sunsets, which would be haven helpful for both agriculture and religious ceremonies. Annual equinox and solstice events are still held here, and you can attend!

We may never be able to answer all of the mysteries that remain here, and maybe that's for the best. Cahokia Mounds are open to the public daily from dawn until dusk. The view from the top of Monks Mound is truly inspirational, so be sure to wear comfortable shoes. For more information, visit the website, and don't forget to give them a follow on Facebook so you can stay up to date on any upcoming events.