Background
Since 1378, the Great Western Schism had divided the Roman Catholic Church; two men claimed to be pope, one at Avignon, the other at Rome. Cossa adhered to the Roman obedience. In 1402 Pope Boniface IX made him a cardinal, and from 1403 to 1408 he administered papal territories as legate in Bologna. Cossa dealt effectively there with financial and military affairs. He displayed the qualities of a skillful and ambitious politician, rather than of a Christian cleric.
Cossa was one of the cardinals from both obediences who deserted their respective popes and convened a general council at Pisa (1409). It was widely believed that only such a council could restore unity to the Church, and many people accepted conciliarism--the theory that a council representing the whole Church was superior to a pope. The Council of Pisa declared the deposition of the Roman pope Gregory XII and the Avignonese pope Benedict XIII and elected a new pope, Alexander V. This move failed to end the Great Western Schism, however, for now there were three papal claimants instead of two. Alexander V was heavily under Cossa's influence, and after he died Cossa was elected to succeed him on May 17, 1410. Only after his election was he ordained to the priesthood. On May 25 he was crowned as John XXIII.
At that time, a war was being fought in Italy between Louis of Anjou and Ladislas of Durazzo, who both claimed the crown of Naples. Cossa sided with Louis, and was present at the Battle of Roccasecca in 1411. In 1413, as Ladislas' troops advanced on Rome, he and his cardinals were obliged to flee northward.
Despite these secular distractions, Cossa took some important actions in church affairs. He elevated such distinguished scholars as the theologian Pierre D'Ailly and the canonist Francesco Zabarella to the rank of cardinal. In 1413, under pressure from the Emperor Sigismund, he reluctantly summoned a new general council. It convened at Constance in November 1414. In hopes of ending the schism, the council demanded that all three papal claimants abdicate, and Cossa promised to do so. In March 1415, however, he fled secretly from Constance to Schaffhausen, and was presently taken into custody. The Council of Constance then convicted him of simony (selling church offices for money), wasting church property and rights, and leading a "detestable and dishonorable life," and on May 29, 1415, declared him deposed. In 1418 he was freed, and the next year he accepted Martin V as pope and was made a cardinal once again. On Nov. 22, 1419, he died at Florence.
Although, of the three papal claimants in his day, Cossa commanded the largest following within the Catholic Church, the Catholic canon law tradition has denied the right of the Council of Pisa to depose his rivals; if that deposition was invalid, the two popes of the Pisan obedience were antipopes (illegitimate claimants). That is why, when Angelo Roncalli was elected pope in 1958 and took the name John, he was called John XXIII.
