One August day in 1987, Brian Campbell was refilling the hole left by a tree stump in his yard in Romford, East London, when his shovel struck something metal. He leaned down and pulled the object from the soil, wondering at its strange shape. The object was small—smaller than a tennis ball—and caked with heavy clay. “My first impressions,” Campbell tells Mental Floss, “were it was beautifully and skillfully made … probably by a blacksmith as a measuring tool of sorts.”
Campbell placed the artifact on his kitchen windowsill, where it sat for the next 10 or so years. Then, he visited the Roman fort and archaeological park in Saalburg, Germany—and there, in a glass display case, was an almost identical object. He realized that his garden surprise was a Roman dodecahedron: a 12-sided metal mystery that has baffled archaeologists for centuries. Although dozens, and perhaps hundreds, of explanations have been offered to account for the dodecahedrons, no one is certain just what they were used for.
The first Roman dodecahedron to intrigue archaeologists was found almost 300 years ago, buried in a field in the English countryside along with some ancient coins. “A piece of mixed metal, or ancient brass, consisting of 12 equal sides,” read the description of the egg-sized object when it was presented to the Society of Antiquaries in London in 1739. The 12 faces had “an equal number of perforations within them, all of unequal diameters, but opposite to one another … every faceing had a knobb or little ball fixed to it.” The antiquarians were flummoxed by the finely crafted metal shell, and what its purpose may have been.
The 1739 dodecahedron was far from the last discovery of its kind. More than 100 similar objects have since been found at dozens of sites across northern Europe dating to around the 1st to 5th centuries CE. Ranging in size from about a golf ball to a bit larger than a baseball, each one has 12 equally sized faces, and each face has a hole of varying diameter. The objects themselves are all hollow.
By the mid-19th century, as more were found, the objects became known to archaeologists as dodecahedrons, from the Greek for “12 faces.” They’re on display today in dozens of museums and archaeological collections throughout Europe, although given how little is known about them, their explanatory labels tend to be brief.
What’s more, they have no paper trail. Historians have found no written documentation of the dodecahedrons in any historical sources. That void has encouraged dozens of competing, and sometimes colorful, theories about their purpose, from military banner ornaments to candleholders to props used in magic spells. The obvious craftsmanship that went into them—at a time when metal objects were expensive and difficult to make—has prompted many researchers to argue they were valuable, an idea that’s supported by the fact that several have been found stashed away with Roman-era coins. But that still doesn’t explain why they were made.