They still don't know what it's for

 

As I have noted many times, archaeologists, both professional and amateur, keep finding ancient relics in England.  Of course, a lot of events happened in England that could provide ancient relics. What is amazing to me is that they are still lying around.  They might be under some soil, or a parking lot (like King Richard III), or in a stream or lake, or even in someone's closet after a day spent picking up little trinkets. But they keep finding them.

In this case, they found an object that is known to be Roman -- but also something for which no definitive use has been found. Also in this case, they were amateur archaeologists.

12-sided Roman relic baffles archaeologists, spawns countless theories

This is what it looks like. What do you think it was used for?

A lot of uses have been suggested, but according to sources, none of these relics are mentioned in any Roman writings. So that might indicate that they were used in some sort of banned religious ritual. 

As the article says:

"Since 1739, some 130 of these objects have been discovered across Northern and Western Europe. While archaeologists have dated the relics to Roman times, they have been baffled by the objects for centuries, with no consensus ever emerging on what they were for. There is no known written description of them in ancient texts; nor do any pictorial references exist."

And we may never know.