John XXIII

John XXIII was the papal name of Baldassare Cossa, who claimed the papacy from 1410 to 1415 during the Western Schism. The Council of Constance deposed him and treated him as an antipope.

Western Schism: A division in the Catholic Church from 1378 to 1417, during which rival lines of popes claimed legitimacy. The competing papal obediences created the political opening for Cossa’s claim.
Council of Constance: An ecumenical council held from 1414 to 1418 that ended the Western Schism and addressed church reform. It summoned Cossa, tried him, and deposed him in 1415.
Antipope: A person who claims or is elected to the papacy in opposition to a pope recognized as legitimate by the Catholic Church. The Catholic Church classifies Cossa as an antipope rather than a legitimate pope.
Constance: A city in present-day Germany where the Council of Constance met from 1414 to 1418. Cossa was detained there after the council deposed him.
Avignon Papacy: The period from 1309 to 1377 when the papal court resided in Avignon rather than Rome. Its aftermath shaped the rival loyalties that persisted into Cossa’s pontificate.
Haec Sancta: A decree of the Council of Constance asserting the authority of a general council over the pope in matters of church unity. Its claim of conciliar authority framed the council’s action against Cossa.
Martin V: The pope elected by the Council of Constance in 1417, whose election is generally treated as ending the Western Schism. His widely recognized election replaced the divided obedience under which Cossa had claimed office.
Florence: An Italian city that became a major center of Renaissance culture and banking. After escaping custody, Cossa sought refuge and support there.
Benedict XIII: A claimant to the papacy during the Western Schism, supported chiefly in Iberia and southern France. He was one of the rival claimants whose removal the Council of Constance sought.
Pisa: An Italian city where cardinals convened a council in 1409 to end the Western Schism. The council at Pisa elected Cossa’s predecessor in the Pisan line and deepened the schism.

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Pope John XXIIIBroader topic: This name’s two historical claimants account for the concept’s ambiguity.