JOHN YANG: On this Native American Heritage Day, we examine a long overlooked marvel of ancient engineering that had been tucked away beneath a golf course near Columbus, Ohio.

Some archaeologists say it's on par with Stonehenge, but its struggle for recognition spanned decades, ending only recently with validation as the state's only World Heritage Site.

Stephanie Sy is back with that story.

BRAD LEPPER, Senior Archaeologist, Ohio History Connection: So we're approaching the avenue, the parallel walls that connect the Observatory Circle with the octagon beyond.

STEPHANIE SY: From the ground where archaeologist Brad Lepper stands, you can't really appreciate its complexity.

It's the view from above that is the view from above that reveals the site in Newark, Ohio's astonishing geometry.

The Octagon Earthworks are composed of vast soil mounts, a perfect 20-acre circle connecting to a perfectly symmetrical 50-acre octagon, large enough to fit four Roman Colosseums.

The intricate design mirrors the moon's 18.6-year journey across the sky, its central axis meticulously aligned to the spot where the moon rises at its northernmost point.

BRAD LEPPER: And they're not just close to being precise.

They're very, very precise.

STEPHANIE SY: What's even more impressive is when it was constructed.

BRAD LEPPER: About 2,000 years ago.

The span of time we're talking about is like 1 C.E.

all the way up to 400 C.E.

That's about the time of the peak of the Roman Empire.

STEPHANIE SY: There are still many unknowns about who these Native American builders were.

It's a long-gone ancient cultural network spread across the Eastern United States that researchers now call the Hopewell.

BRAD LEPPER: These people lived in scattered little communities, and thousands and thousands of those communities probably came together here, but they have left no written records.

I think this was like Mecca or like Jerusalem as a pilgrimage center, but, without a Koran or a Bible, we don't have the knowledge of who these ceremony leaders were.

What was the vision that compelled people to come here for hundreds of miles?

STEPHANIE SY: But, to Lepper, who spent almost 40 years studying them, the earthworks themselves speak volumes about their builders, who lived roughly 1,500 years before Galileo.

BRAD LEPPER: They were geometers, mathematicians.

They were astronomers.

They were geniuses.

I mean, they were soil scientists.

They knew what soils to use to build enduring earthworks.

GLENNA WALLACE, Chief, Eastern Shawnee Tribe of Oklahoma: When I go to those mounds, I can hear those ancestors singing.

They didn't have steel.

They didn't have concrete.

They didn't have metal.

What they had was mother earth.

STEPHANIE SY: Glenna Wallace is the chief of the Eastern Shawnee Tribe of Oklahoma, descendants of the Hopewell people.

They were forced out of Ohio after the passage of the Indian Removal Act of 1830.

GLENNA WALLACE: Ohio truly didn't have a voice, a Native American voice, a Native American presence.

STEPHANIE SY: Without that voice, these mounds were buried over time beneath railroads, development and housing.

Today, of the dozens of Hopewell earthworks that once stood across Ohio, less than half remain preserved.

GLENNA WALLACE: Will they never be content until they have eliminated every trace of our ancestors?

That's what's going through my mind.

STEPHANIE SY: The Octagon Earthwork was spared only because of how the site was used.

BRAD LEPPER: This is part of the golf course infrastructure.

There was even a time when they teed off from the top of the mound.

STEPHANIE SY: For more than a century, the site was taken over by a golf course.

BRAD LEPPER: It was such a contrast to have golfing going on in a place that's like Notre Dame Cathedral or something.

It always was jarring.

GLENNA WALLACE: The first thought that came to my mind was the biblical scripture, father, forgive them, for they know not what they do.

Earthworks are sacred to us.

And to then look out and see that those mounds had a golf course on top of them, I can't explain the disappointment, the hurt, the lack of respect that I felt on behalf of my ancestors.

STEPHANIE SY: Over the years, the golf course became a members only country club, which limited access to the historic site.

JENNIFER AULTMAN, Director of Historic Sites and Museums, Ohio History Connection: It was very much that sort of private aspect that made it really challenging for us even to do things like research.

STEPHANIE SY: Jennifer Aultman is the director of historic sites and museums at Ohio History Connection, which hatched a plan for the long overlooked ancient mounds more than two decades ago.

JENNIFER AULTMAN: There was sort of this thought that, like, this place is as significant as Stonehenge and Machu Picchu, and nobody seems to understand that.

And if it was a World Heritage Site, like, people would have to understand that.

STEPHANIE SY: But to become a World Heritage Site isn't easy.

It's a list that includes the Great Wall of China and the Pyramids of Giza.

It took Ohio History Connection more than 20 years, including a lengthy legal battle for control of the site, before the moment arrived in 2023.

DR.

ABDULELAH AL-TOKHAIS, World Heritage Committee: Adopted.

Congratulations to the United States, America.

STEPHANIE SY: At the World Heritage Committee hearing in Riyadh, Saudi Arabia, eight of Ohio's Hopewell mounds were put on the list.

JENNIFER AULTMAN: The gavel came down, and it was in that moment a World Heritage Site.

That was moving enough.

But to be in that room with representatives from all over the world and have Chief Glenna, whose people were forcibly removed from Ohio, speak, that was the moment that it really came home, like, how important this was that we did this.

GLENNA WALLACE: They were not just geniuses.

They were uncommon geniuses.

Their genius lives on today in many descendant tribes.

STEPHANIE SY: What do you think the significance is of having it be designated as a World Heritage Site?

GLENNA WALLACE: It certainly gives us as Native Americans a wonderful feeling of pride.

And I am so proud of the changes that are occurring in Ohio.

The people are beginning to recognize what they have in their communities, and they want to do the right thing.

There was just a lack of knowledge, a lack of information.

STEPHANIE SY: Earlier this year, Octagon Earthworks opened to the public for the first time as a World Heritage Site.

Visitors poured in, and they have kept coming.

And what they learn and see here may contribute to a fuller understanding of Native American civilizations.

BRAD LEPPER: For so long, our society has regarded Indians as savages.

They were here in the way.

They had to be removed and forcibly removed into the West so that these lands could be civilized.

But the irony of that is that there's evidence of this wonderful civilization that was here 2,000 years before Europeans got here.

STEPHANIE SY: An ancient astronomical observatory in Ohio that will now be preserved for the ages.

For the "PBS News Hour," I'm Stephanie Sy.