Bull of Antipope John XXIII found in Mierzyn, Central Poland

In 2021, during excavations of the knight’s manor house at Mierzyn, which belonged to the Nagodzice family, a lead bull of theantipope John XXIII (1410-1415) was found. The seal was discovered in the area of the economic hinterland, a few hundred metres south of the stronghold. This is the second archaeological find of a bull of this antipope from the territory of Poland. The article discusses the object in relation to other finds of this kind and in the context of the history of the medieval knight’s seat in Mierzyn.