Pope Gregory XII (1406–1415) resigned in 1415 in order to end the Western Schism, which had reached the point where there were three claimants to the Papal throne: Roman Pope Gregory XII, Avignon Antipope Benedict XIII, and Pisan Antipope John XXIII. Before resigning he formally convened the already existing Council of Constance and authorized it to elect his successor.


I was afraid of this. This was not a normal papal resignation. I'm not sure there ever has been such.