Since 1739, roughly a hundred of these Roman dodecahedra have been found in sites ranging from Wales to Hungary, but mostly in Germany & France. Some are bronze, and some are made of stone.
No mention of them has been found in contemporary accounts or pictures of the time. Speculated uses include candlestick holders (wax was found inside one example); dice; survey instruments; devices for determining the optimal sowing date for winter grain; gauges to calibrate water pipes or army standard bases. Use as a measuring instrument of any kind seems to be prohibited by the fact that the dodacahedrons were not standardised and come in many sizes and arrangements of their openings. It has also been suggested that they may have been religious artifacts of some kind. This latter speculation is based on the fact that most of the examples have been found in Gallo-Roman sites. Several dodecahedrons were found in coin hoards, providing evidence that their owners considered them valuable objects.
Hat tip to Karen L. Myers.