The 2,000-year-old mystery mounds of the United States

The Hopewell Ceremonial Earthworks are a testament to indigenous sophistication, built by a mysterious civilisation that left no written records.

As dozens of eager tourists and I followed a guide along a grassy mound, autumn leaves crackled under our shoes. We came to a halt when we came to the opening of a turf-topped circle formed by another wall of mounded earth. We were at The Octagon, part of the Hopewell Ceremonial Earthworks, a vast network of hand-built hills spread across central and southern Ohio that date back up to 2,000 years. Indigenous people would travel hundreds of miles to The Octagon to participate in shared rituals and worship.

“There was a sweat lodge or some kind of purification place there,” our guide Brad Lepper, senior archaeologist for the Ohio History Connection’s World Heritage Program, explained (OHC), as he indicated the circle When I went inside, I saw a perfectly manicured lawn – a putting green. A tall flag with a hole in the centre.

Currently, the Octagon is being used as a golf course.

All of these prehistoric ceremonial earthworks in Ohio were built by the Hopewell Culture, a network of Native American societies that gathered from as far away as Montana and the Gulf of Mexico between roughly 100 BCE and 500 CE and were linked by a network of trade routes. Their earthworks in Ohio are made up of shapes like circles, squares, and octagons that are frequently connected to one another. Archaeologists are only now starting to comprehend the complexity of these engineering marvels.

Built with incredible mathematical precision and a complex astronomical alignment, These are the world’s largest geometrical earthworks that were not constructed as fortifications or defensive structures. And, while most people have never heard of the sites or their creators, that may soon change.

The Octagon alone could house four Roman Colosseums.

The US Department of the Interior has proposed eight Hopewell earthworks for listing as a Unesco World Heritage site in 2023. These include The Great Circle and The Octagon in Newark, Ohio, as well as Fort Ancient, Ohio’s first state park (not an actual fort). The Hopewell Culture National Historical Park includes the following five sites: Mound City, Hopeton Earthworks, High Bank Works, Hopewell Mound Group, and Seip Earthworks..

Lepper informed me The Octagon and The Great Circle were once part of a larger Hopewell complex spanning 4.5 square miles and linked by a network of roads lined with earthwork walls. There is an immediate sense of scale when walking through both sites today. The Great Circle, which houses the Hopewell Ceremonial Earthworks Museum, is 1,200 feet in diameter. Its walls reach up to 14 feet in height and are framed on the inside by a deep ditch. The Great Circle was once linked to a square and a burial ellipse, with only a portion of the square visible today. The Octagon covers 50 acres and is connected to the 20-acre Observatory Circle. a large earthwork circle for gatherings and rituals related to night sky observation

“You could fit four Roman Colosseums inside The Octagon,” said Lepper. Stonehenge would fit within the small circle that is now a putting green. He added that indigenous workers built these earthworks without modern tools 2,000 years ago, digging up soil with pointed sticks and hauling it on their backs in wicker baskets. According to one estimate, they moved seven million cubic feet of dirt.

The Hopewell Culture’s achievement, however, is not simply in creating large, precise shapes without the vantage point of hills for an aerial view. They also incorporated a type of hidden geometry into these structures. Until the mounds were measured and compared, it was assumed that the builders lacked mathematical and geometrical sophistication, as there are no written records to back up their claims. However, it was eventually discovered that they took precise measurements across their earthworks and connected them in unexpected ways.

The Great Circle’s circumference “is equal to the perimeter of the perfect square to which it was connected,” according to Lepper, and “the area of that perfect square is equal to the area of the [Observatory Circle] that is connected to The Octagon.”

“If you draw a square inside The Octagon by drawing a line from alternate corners of The Octagon, the sides of that square [1,054ft] are equal to the diameter of the circle to which it’s attached [1,054ft],” he continued.

Archaeologists have discovered numerous examples of this interplay between earthworks. According to Lepper, the 1054ft measurement is found in other indigenous earthworks across the country and served as a common unit of measurement.

While scholars were astounded by the Hopewell Culture’s geometrical and mathematical knowledge, another level of sophistication emerges when the layers are peeled back further: astronomical alignment.

Ray Hively (a physicist and astronomer) and Robert Horn (a philosopher) of Earlham College in Indiana decided to visit The Octagon and its attached Observatory Circle in the 1980s. They wondered if these earthworks were also aligned to a solar calendar because astronomical monuments like Stonehenge had received so much attention.

Hively and Horn discovered no solar connections, but they did consider another possibility: the lunar cycle.

“We thought deliberate lunar alignments unlikely at Newark,” they wrote, because while the Sun can be tracked over a year, the lunar cycle takes 18.6 years to complete. Nonetheless, the lunar cycle corresponded to the location of the Observatory Mound at The Observatory Circle. Every 18.6 years, the Moon rises over the exact centre of The Octagon in the distance.

“Astronomical alignments are only relevant and useful if they somehow tie the celestial orbs to belief systems and understandings of life,” said Timothy Darvill, a Bournemouth University professor of archaeology who has studied both Stonehenge and the Hopewell Ceremonial Earthworks. “The ceremonies centred on the observation of the skyscape may serve a secondary purpose in terms of fostering community.”

That ancient community and culture are included in the Unesco case.

According to Jennifer Aultman, director of historic sites and museums at Ohio History Connection and the Ohio lead for Unesco consideration, a Unesco site must demonstrate “outstanding universal value.” She stated that one criterion for this is that “these are masterpieces of human creative genius,” which is where these mathematical, geometrical, and astronomical features come into play. “The other is that they bear truly exceptional testimony to the cultural tradition that produced them,” says the author.