Amateur archaeologists in England have unearthed one of the largest Roman dodecahedrons ever found, but mystery surrounds what it was actually used for.

The 12-sided object is one of just 33 known to exist in Roman Britain, and one of approximately 130 in the world. It is considered “one of archaeology’s great enigmas,” according to the Norton Disney History and Archaeology Group, an amateur group based in the English region of Lincolnshire where it was found in June.

Measuring about 8 centimeters (3 inches) across, the dodecahedron is hollow and covered with 12 holes of varying sizes.

The 1,700-year-old object will be displayed at the Lincoln Museum from May 4 until early September.

“It’s a real pleasure to have the Norton Disney dodecahedron joining us… just a stone’s throw from where it was found,” Andrea Martin, exhibitions and interpretations manager at the museum, said in a Lincolnshire County Council press release. “To have the opening of the display coincide with the Lincoln Festival of History is a real coup.”

The release describes the dodecahedron as “one of the largest examples” discovered.

However, experts still aren’t sure exactly what the Romans used the dodecahedron for.

“It is completely unique,” said Richard Parker, secretary of the Norton Disney History and Archaeology Group, adding that no similar objects have ever been found. He said that, unlike other dodecahedra, this one is undamaged.

“Ours is absolutely in a fabulous condition. It’s complete, undamaged, and it clearly was considered of great value by whoever made it and by those that used it,” Parker said. “So there must have been a very important reason for it to be deposited in the ground in the way that it was.”

Parker told CNN there are no descriptions of the dodecahedron in Roman literature, and they have not been depicted pictorially in mosaics. There are also several features that make it difficult to discern what its intended purpose was. All of the dodecahedra are of different sizes, meaning they were not used for measurement, he said. Because it is undamaged with no signs of wear, it is unlikely to have been a tool, Parker added.

Parker’s group does have one working theory, however.

“Most likely they were some form of religious or ritual object,” he said. “The Romans were a very superstitious lot, and generally required signs to allow them to make decisions in their daily lives.”

One indication supporting that idea is that the object was found near a small Roman mounted rider god figurine with “strong religious connections,” Parker said. The artifact was discovered in 1989 by metal detectorists, and the figurine is “often found on temple sites.”

The organization plans to return to the dig site later this year to conduct further excavations, which Parker hopes will help establish context on how the area was used. Parker said he is optimistic that the mystery will be solved because this dodecahedron was found in an archaeological excavation area, whereas “many of those that were found 200 or 300 years ago had no context to where they were found.”

“It is quite a complex story to tell that we’re just starting to tease out,” he added.