JOHN XXIII. (Baldassare Cossa), pope, or rather anti-pope from 1410 to 1415, born of a good Neapolitan family, was a cor sair before entering the service of the church under the pontificate of Boniface IX. He won the cardinal's hat and the legation of Bologna. On June 29, 1408, he and seven of his colleagues broke away from Gregory XII., and together with six cardinals of the obedience of Avignon, who had in like manner separated from Benedict XIII., they agreed to aim at the assembling of a gen eral council, setting aside the two rival pontiffs, an expedient which they considered would put an end to the great schism of the Western Church, but which resulted in the election of yet a third pope. This act was none the less decisive for Baldassare Cossa's future. Alexander V., the first pope elected at Pisa, was not perhaps, as has been maintained, merely a man of straw put forward by the ambitious cardinal of Bologna; but he reigned only ten months, and on his death (May 4, 1410), Baldassare Cossa succeeded him. He seems to have received the unani mous vote of all the 17 cardinals gathered together at Bologna (May 17). He took the name of John XXIII., and France, England, and part of Italy and Germany recognized him as head of the Catholic church.
The struggle in which he and Louis II. of Anjou engaged with Ladislaus of Durazzo, king of Sicily, and Gregory XII.'s chief protector in Italy, at first went in John's favour. After the brilliant victory of Roccasecca (May 19, 1411) he dragged the standards of Pope Gregory and King Ladislaus through the streets of Rome. But he eventually abandoned the cause of Louis of Anjou, and recognized Ladislaus, his former enemy, as king of Naples. Ladislaus did not fail to salute John XXIII. as pope, abandoning Gregory XII. (June 15, 1412). This was a fatal step : John XXIII. was trusting in a dishonest and insatiable prince. John convened a sparsely attended council in Rome which held only a few sittings, and on March 3, 1413, he adjourned it till December. On Dec. 9 he issued the bull convening the council of Constance, under pressure from Sigismund, king of the Romans. Meanwhile (June 8, 1413) Ladislaus had turned against John, had sacked Rome, and expelled him.
On Nov. 5, 1414, John opened the council of Constance, where, on Christmas Day, he received the homage of the head of the empire, but where it was soon evident that his position was un tenable. He had to take a solemn oath to abdicate if his two rivals, Benedict XIII. and Gregory XII., would do the same.
On the night of March 20-21, having donned the garments of a layman, with a cross-bow slung at his side, he escaped from Con stance, and took refuge first in the castle of Schaffhausen, then in that of Laufenburg, then at Freiburg-im-Breisgau, and finally at Brisach, whence he hoped to reach Alsace, and doubtless ulti mately Avignon, under the protection of an escort sent by the duke of Burgundy. The news of the pope's escape was received at Constance with an extraordinary outburst of rage, and led to the subversive decrees of the 4th and 5th sessions, which pro claimed the superiority of the council over the pope. Duke Fred erick of Austria was compelled to surrender John, who was brought back to Freiburg. He was suspended from his functions as pope on May 14, 1415, and deposed on May 29.
However irregular this sentence may have been from the canonical point of view (for the accusers do not seem to have actually proved the crime of heresy, which was necessary, accord ing to most scholars of the period, to justify the deposition of a sovereign pontiff), the condemned pope was not long in confirm ing it. Baldassare Cossa, now as humble and resigned as he had before been energetic and tenacious, on his transference to the castle of Rudolfzell admitted the wrong which he had done by his flight, refused to bring forward anything in his defence, acquiesced entirely in the judgment of the council which he declared to be infallible, and, finally, ratified mote proprio the sentence of deposition, declaring that he freely and willingly renounced any rights which he might still have in the papacy. This fact has subsequently been often quoted against those who have appealed to the events of 1415 to maintain that a council can depose a pope who is scandalizator ecclesiae.
Cossa was held prisoner for three years in Germany, but in the end bought his liberty (1418) from the count palatine. He then threw himself on the mercy of the legitimate pope. Martin V.
appointed him cardinal-bishop of Tusculum, a dignity which Cossa only enjoyed for a few months. He died on Dec. 22, 1419, and all visitors to the Baptistery at Florence may admire, under its high baldacchino, the sombre figure sculptured by Donatello of the dethroned pontiff, who had at least the merit of bowing his head under his chastisement, and of contributing by his passive resignation to the extinction of the series of popes which sprang from the council of Pisa.