What it was used for was not shown.
Debated. No one has settled the purpose.
At Kortessem, in Belgium, a bronze piece of a Roman dodecahedron was found. A whole one has twelve five-sided faces, a round hole in each face, and often small balls at the corners. This piece is about 5 to 6 centimetres across. The page says these objects date from the 2nd or 3rd century AD. It also says this piece is about 1,600 years old. Those ages do not agree.
People still argue what a dodecahedron was for. The page gives many ideas, and says none of them fits every part.
https://www.ancient-origins.net/news-history-archaeology/roman-dodecahedron-0017954