A man using a metal detector to search for World War II relics found a medieval artifact in Poland, a local museum said. 

The Museum of the History of the Kamień Land announced the “unbelievable” find on Tuesday. According to the museum’s news release, a man identified as Jacek Ukowski found a piece of a “medieval leaded pope’s bull.” 

A papal bull is a type of public decree or charter issued by a pope during their reign. Many ancient papal bulls included a metal seal, which would have made it recognizable to a metal detector. 

The fragments of the bull were inscribed with a Roman numeral and a partial name. Because the inscription is not “fully preserved,” the museum said it could not be used to identify which pope the relic might be related to, but dated the item to somewhere between 1303 and 1352. 

The location of the find made it even more surprising. There are a number of areas in Poland where papal bulls have been found and traced back to their issuers, the museum said, but rather than being found near a church site or in a city center, these fragments were found alongside a set of train tracks. The museum said there are multiple ways this could have happened, from the bull just being lost in transit or even deliberately destroyed and abandoned, but there is no way to tell what exactly led to it being buried near the tracks.

“This will probably be another unsolved mystery for us. It’s likely that we won’t find an answer to it anymore. Especially that the bull only remained in a fragment,” said the museum. 

This isn’t the first time Ukowski has found a papal bull. He made a similar discovery in February, according to the museum and a local newspaper. Ukowski donated both relics to the museum. Overall, it’s the third such artifact found in the region recently, the museum said.