Amateur archaeologists found a mysterious 12-sided object from the Roman Empire that experts can't explain

• An amateur archaeology group found a mysterious dodecahedron near an ancient Roman villa.
• The purpose of these 12-sided objects is unknown, though many theories have been suggested.
• The complex crafting process suggests they were likely custom-made and expensive.

Down a tree-lined road 100 miles north of London lies an open field where a Roman villa once stood about 2,000 to 1,700 years ago.

Amateur archaeologists with the Norton Disney History and Archaeology Group have been excavating its remains, including a bathhouse, gatehouse, and ancient tiled mosaic floors for the last few years when they made a miraculous discovery.

Last year, a dozen volunteers were digging up a field about half a mile from the villa when a cry went up, Richard Parker, the group's secretary, told Business Insider.

The archaeologists had mostly been finding masonry, some animal bones, and a lot of pottery. But Richard Watts, one of the volunteers, was holding something unique.

It was a small metal object, about the size of a softball, with holes in each of its 12 sides and covered with small knobs.

"We realized we'd found something really quite significant pretty quickly," Parker said. Though he'd never seen one in person, Rob Evershed, a member of the group, recognized the hollow, rounded object as a Roman dodecahedron.

Everyone started Googling on their phones. Work stopped as they tried to figure out what to do next, Parker said.

Only around 130 dodecahedrons have ever been found. The first known one was discovered in 1739 in Hertfordshire, England.

This latest find is the first dodecahedron ever uncovered in England's Midlands region, the BBC reported. The British broadcast recently featured the object on an episode of "Digging for Britain," a show about archaeology. And England's Lincoln Museum put the object on display for the first time last weekend during its Festival of History.

No one knows the purpose of the dodecahedron

A toy? A tool? A religious relic? Once the group had identified it as a dodecahedron, they still had no idea what exactly it was. In fact, no one really knows.

"The fact that many of them were found before scientific excavation started in the 20th century does hinder our understanding of them," Frances McIntosh, an archaeologist with English Heritage who specializes in Roman artifacts, told Business Insider via email.

There often aren't detailed records of their excavation sites.

Over the centuries, more have turned up in the northwestern provinces of the Roman Empire in present-day Belgium, Croatia, France, Germany, Great Britain, Hungary, Luxemburg, the Netherlands, and Switzerland, McIntosh said.

However, she noted that dodecahedrons haven't been found in Italy, Spain, Africa, or Turkey. That regionality adds to their mystery.

Made of a copper alloy, the 12-sided dodecahedrons don't have an obvious function. They come in many sizes, meaning they likely weren't used as a measurement tool. They're somewhat fragile and couldn't withstand heavy use, an archaeologist told The Washington Post.

Some scholars suggest dodecahedrons have religious significance or played a role in rituals. Other guesses range from a candle holder to surveying equipment. Their locations don't offer many clues, either.

"They have been found in all sorts of places," McIntosh said. People have dug up dodecahedrons at military camps, a temple, public baths, a theater, and a tomb, to name a few.

Dodecahedrons may have been custom-made

Parker thinks it would've taken an expert to make the dodecahedron that the Norton Disney group found. An analysis of the material found it's 75% copper, 18% lead, and 7% tin.

"The composition is fairly unusual," Parker said. "Having such a high lead content, it would've required a lot of skill to pour this particular alloy into the mold because it would've been very sticky."

McIntosh agrees an experienced craftsperson likely made it. "As this is a hollow item, it would have been a very complex process," she said.

That complexity means they wouldn't have been cheap. "They would have been expensive items," McIntosh said, "likely bespoke commissions."

The dodecahedrons' many mysteries make them fascinating, Parker said. The group plans to return to the site this year to look for more objects and possibly new clues to the dodecahedron's significance.