Look, Romans had historians, sort of. They knew about ancient (to them) civilizations, and the mysterious artifacts they had left behind. They also had the equivalent of modern billionaires. And they even had a sense of humour (a bit rude, maybe, judging by the graffiti in Pompeii, but a sense of humour nonetheless).

What they did not have, however, was the vast variety of entertainment we have today, so they probably got bored.

Now, imagine an extremely wealthy, extremely bored Roman, who’s been reading about the mysterious hieroglyphs of ancient Egypt, and been wondering about what the people of future millennia will say about Rome… and in his boredom he comes up with the perfect, most funny way to prank them.

So he seeks a good engineer and has him come up with something somewhat complex yet easy to mass produce, that will withstand the ravages of time, and which looks like it must have had a purpose, yet is actually completely useless. Then he takes the design to several metalsmiths and pays them to make a few thousand of the things, and pays a few dozen men to travel the empire dropping the things in inconspicuous places where no one will notice them for centuries, and spends the rest of his life amusing himself thinking about the theories future historians might come up with to explain the damn things.

That is what I believe Roman dodecahedrons must have been for.