In 1378, under Pope Gregory XI, the papacy returned to Rome, ending the Avignon Papacy. After his death, however, Pope Urban VI was considered so overbearing that the cardinals also elected Pope Clement VII, who established himself at Avignon. This split, known as the Papal Schism or Western Schism, would last until 1417, and at times the Catholic Church had three simultaneous popes.
Approximately fifteen years into the schism, seeking a solution the problem, the theologians at the University of Paris had large chest placed into the cloister of the Mathurins. They asked that anyone with a solution to the schism write it down and place it into a slot in the lid of the chest. All in all, over ten thousands solutions were suggested, which were read through by fifty-five professors in a desperate attempt to find an acceptable solution.
The proposals were mostly categorized into three groups. One group proposed that all current popes abdicate and a new one be elected. Another proposed arbitration between the popes that would result in a single, legitimate pontiff. The third called for a new convention of the Catholic cardinals who would elect a new pope, delegitimizing the previous ones.
The final solution was a combination of the first and third proposals. Pope Gregory XII, one of the Roman popes, excommunicated the Avignon pope and resigned, allowing the cardinals to elect Martin V as pope. Some still supported the Avignon and Pisa popes, but Martin V had the vast majority of Catholic support, and with his election, the Papal Schism essentially ended.