The 1378 papal conclave, held from 7–9 April 1378, was the papal conclave which was the immediate cause of the Western Schism in the Catholic Church. The conclave was one of the shortest in the history of the Catholic Church. The conclave was also the first held in the Vatican and in Old St. Peter's Basilica since 1159 (the elections and conclaves in Rome prior to the Avignon Papacy having been held mostly in the Basilica of St. John Lateran).
Pope Gregory XI died on 26 March 1378, in Rome, having returned from Avignon to pursue his territorial interests in the Papal States during the War of the Eight Saints. Although the French cardinals constituted a majority of the College of Cardinals due to the preceding Avignon Papacy, they succumbed to the will of the Roman mob, which demanded the election of an Italian pontiff. They elected Bishop Bartolommeo Prignano, who took the name Pope Urban VI. This is the most recent time a non-cardinal has been elected pope.
Proceedings
Before his death, Gregory XI substantially loosened the laws of the conclave: he instructed the cardinals to begin immediately after his death (rather than waiting the nine days prescribed by the Ordo Romanis) to prevent "factional coercion", he gave the cardinals permission to hold the conclave outside of Rome and move it as many times as necessary, and also seemingly suspended the two-thirds requirement, replacing it with "the greater part" (an ambiguous statement, in the original).
The cardinals were divided into three factions: the first constituting the four Italian cardinals (two Romans, one Florentine, and one Milanese), the second constituting the seven "Limoges" cardinals (referred to individually as "Limousins"), and the third constituting the five remaining French cardinals. The conclave was delayed one day because of a violent storm, and thereafter the seven Limoges cardinals wishing to leave Rome as Gregory XI had authorized them to were persuaded by the others that such an act would place the college in even more danger. It was midnight on the second day before the servants of the cardinals succeeded in clearing the Old Basilica of those not permitted to remain in the conclave.
According to the Catholic Encyclopedia, even Robert of Geneva (future Antipope Clement VII) and Pedro Martínez de Luna y Gotor (future Antipope Benedict XIII)—the two claimants of the Avignon line during the ensuing Schism—were among those who voted for Prignano. Prignano had previously lived in France, which may have softened the blow of his election to many of his French electors. The selection was supposedly "unanimous", with the exception of Giacomo Orsini, who claimed that he was not "free" enough to vote.
Prignano was accompanied by several other prelates (to conceal the identity of the selected candidate) to the Vatican to accept his election. To further the confusion, Orsini gave the Habemus Papam without identifying Prignano. Upon the conclusion of the election, the Roman mob entered the site of the conclave, under the impression that an aged Roman cardinal Tebaldeschi (who had been left in possession of the papal insignia) had been elected, an impression that the remaining cardinals did not disabuse them of as they fled to their personal quarters. The remaining cardinal informed the crowd of the election of Prignano who was hiding in the "most secret room" until his election could be announced.
Cardinal electors
Sixteen of the twenty-three active cardinals took part in the conclave. Two possible other cardinals—Piero Tornaquinci and Pietro Tartaro—were not accepted into the ranks of the college for the election. Six more cardinals remained in Avignon, and Jean de la Grange was absent as well.
Aftermath
The following September, the French cardinals reunited in Avignon, moved to Fondi, and elected Antipope Clement VII, who gained the support of all thirteen of his electors (at the time the entire College numbered twenty-two due to the death of Francesco Tebaldeschi).