Although today it may seem anodyne, there was a period in history when there was not only one Pope, but up to three simultaneously. It happened during the 14th and 15th centuries with the outbreak of the Great Western Schism, a period of confrontation in the Catholic Church that resulted in the existence of three simultaneous papacies, each one claiming its legitimacy.
One of these was that of Pedro Martinez de Luna, known as Pope Luna or Benedict XIII, elected by the obedience of Avignon in 1394 and legitimized by the kingdoms of Aragon, Castile, Navarre and Scotland, in parallel to the papacy of Rome.
Over time, however, his support waned in Europe, especially after the Council of Pisa in 1409, which attempted to resolve the schism by electing a third pope, but only added to the confusion.
The Western Schism was a period of great confusion and crisis for the Catholic Church, lasting almost 40 years (1378-1417), during which as many as three popes coexisted: one in Rome, one in Avignon and a third in Pisa. The papacy of Benedict XIII largely lacked broad support outside the Crown of Aragon and some faithful territories.
As a consequence, various sectors of the Church proposed to Benedict XIII to renounce the papacy in order to resolve the schism that reigned in Catholicism at that time. The Council of Constance (1414-1418) was decisive: it achieved the resignation of the rival popes of Rome and Pisa, and excommunicated Benedict XIII, who refused to abdicate.
Eventually, Martin V was elected as the only legitimate pope, ending the schism for most of Christendom, although Pope Luna continued to consider himself the true pontiff until his death.
Pope Luna rejected the idea of resigning and, in order to consolidate his power, decided to take refuge in the castle of Peniscola, which was part of the Crown of Aragon, where he was still recognized as pope, remaining there from 1411 until his death in 1423.
Regarding the expression “to remain in his thirteen”, it is true that the most popular theory links it to the obstinacy of Benedict XIII, who, despite the pressures, remained firm in his papal title of Benedict XIII and in his claim to the pontificate.
However, there are other theories about the origin of the phrase, such as its possible relationship with an ancient card game or with the thirteen principles of faith of Judaism, although the link with Pope Luna is the most widespread and accepted in Spanish popular culture.
Thus, Luna remained “in his thirteen”, that is, in his papal name of Benedict XIII, defending his legitimacy until the end. This attitude gave rise, according to the most widespread version, to the expression that today is used to describe people who are immovable in their convictions, even if everyone contradicts them.