This should be "What Is It? Game 184" - but we don't have an answer. Nobody does.
It’s dated from somewhere around the second and third century AD, and has been popping up everywhere in Europe. Archeologists have found the majority of them in France, Switzerland and parts of Germany where the Romans once ruled. But its use remains a mystery, mostly because the Romans who usually kept meticulous accounts make no mention of it in records. And with sizes varying from 4 to 11 cm, and some bearing decorative knobs, it only gets harder to pinpoint a function.
About a hundred of these have been found. Suggested uses include a gambling or game die, a candleholder, a staff decoration, a survey instrument, a toy, a calibration device, or a religious object.
Your guess is as good as theirs.
Link and followup link. Photo: Portable Antiquities Scheme, British Museum. Additional photos at Wikipedia.
"After the Demiurge had used the first four perfect bodies for the elements, says the Timaeus, he had the dodecahedron left over, and he used it for the frame of the whole. There is no need to go into the reasons, geometrical and numerological, which fitted the "sphere of twelve pentagons," as it was called, for the role. What counts here: it was the whole, the cosmos, that was meant."
de Santillana & von Dechend, Hamlet's Mill