A Mystery, Perhaps Forever

Dodecahedrons have been found all over Northern Europe in former Roman encampments, but today no one knows for sure what they were used for:

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...

But unless someone also finds an instruction manual—and after more than 1500 years, that seems doubtful—the Roman dodecahedrons will continue to baffle, and fascinate, for many years to come.