Metal detectorist Jacek Ukowski was walking along the railroad tracks in the Polish village of Wysoka Kamieńska. He was looking for artifacts from World War II. Instead, he stumbled upon something much, much older: the fragment of a lead seal from the Middle Ages.

Engravings on the seal—some Roman numerals, part of a name, and the inscription “PP,” which stands for “Pater Pastorum”—suggest it was used to sign papal bulls: decrees from the leader of the Roman Catholic Church, authenticated by signatures pressed into hot wax. Bulls were issued for all sorts of reasons: to introduce or erase theological doctrines, settle conflicts between other religious groups, and even to denounce previous popes.

Employees at the Kamień Land History Museum, located not far from where the seal was discovered, estimate the artifact to be around 650 years old. Because the name on the seal is incomplete, it is difficult to tell which pope would have used it, but possibilities include Benedict XI, Clement V, Benedict XII, and Clement VI, whose collective rule spanned from 1303 to 1352.

Jacek Ukowski in the field where he found the seal. Photo courtesy of the Kamień Land History Museum.

“We don’t know where the seal came from,” Ukowski told Science in Poland. “Maybe it was transported with the soil from another area, in the construction of a new road.” Another possibility is that the lead seal was abandoned after being damaged. Before this, it might have passed through the hands the bishops of Kamień, who lived in a castle in the nearby town of Golczewo. Alternatively, it may have been destroyed on purpose.

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

A fragment of the papal seal. Photo courtesy of the Kamień Land History Museum.

Regardless of its origin, the seal makes for a rare find. “Only a dozen or so [objects] of this type have been discovered in the country, and they are considered unique,” Grzegorz Kurka, director of the Kamień Land History Museum, told Science in Poland. Others have been found near the Polish cities of Gdańsk, Kraków, Grodno, Nowy Targ, Grzybowo, and Mierzyn.

In total, three papal seals have been found near Wysoka Kamieńska. This particular one is the second to be found this year, as well as the second to be found by Ukowski’s metal detector. The first seal, which was found in 2020 in a field near Kamień Pomorski, dates back to the reign of Benedict XII, who headed the Catholic Church from 1484 to 1492.

All three seals are currently on display at the Kamień Land History Museum, making its collection the second largest in the country.