A rare papal bull of the 15th-cent. antipope Benedict XIII was unearthed by archaeologists at the Grodno Castle, South-West Poland.

The objects is a seal from a document issued by the office of Benedict XIII (1328-1423), considered an antipope by the Catholic Church. The artefact was originally attached by a linen cord to a document. The seals did not change throughout the whole Middle Ages, depicting St Peter and St Paul and containing the name of the current pope. The found artefact was compared with other examples of the seals produced by the office of the same pope, and confirmed as authentic. At present it is unknown how the seal got to the site of excavations, neither to which document it was attached to. The researchers suppose it might have been a confirmation of a decree or appointing a local official to his office.

(after RMF FM, RMF24 & Bartłomiej Paulus)