respective churches, as the tit-for-tat excommunications, even had they been valid, would have applied to the named persons only. At the time of the excommunications, many contemporary historians, including Byzantine chroniclers, did not consider the event significant. Post-schism period Second Council of Lyon (1272–1274) On 31 March 1272, Pope Gregory X convoked the Second Council of Lyon to act on a pledge by Byzantine emperor Michael VIII Palaiologos to reunite the Eastern church with the West. Wishing to end the East-West Schism that divided Rome and Constantinople, Gregory X had sent an embassy to Michael VIII, who had reconquered Constantinople, putting an end to the remnants of the Latin Empire in the East. On 29 June 1274 (the Feast of Peter and Paul, the patronal feast of popes), Gregory X celebrated Mass in St John's Church where both sides took part. The council declared that the Roman church possessed "the supreme and full primacy and authority over the universal Catholic Church." The council was seemingly a success, but did not provide a lasting solution to the schism. Michael's death in December 1282 put an end to the union of Lyon. His son and successor Andronikos II Palaiologos repudiated the union. Reformation The primacy of the Pope was again challenged in 1517 when Martin Luther began preaching against several practices in the Catholic Church, including some itinerant friars' abuses involving indulgences. When Pope Leo X refused to support Luther's position, Luther claimed belief in an "invisible church" and called the pope the Antichrist. Luther's rejection of the primacy of the Pope led to the start of the Protestant Reformation, during which numerous Protestant sects broke away from the Catholic Church. The Church of England also broke away from the Catholic Church at this time, although for reasons different from Martin Luther and the Protestants. First Vatican Council The doctrine of papal primacy was further developed in 1870 at the First Vatican Council, where ultramontanism achieved victory over conciliarism with the pronouncement of papal infallibility (the ability of the pope to define dogmas free from error ex cathedra) and of papal supremacy, i.e., supreme, full, immediate, and universal ordinary jurisdiction of the pope. The First Vatican Council's dogmatic constitution Pastor aeternus declared that "in the disposition of God the Roman church holds the preeminence of ordinary power over all the other churches." This council also affirmed the dogma of papal infallibility, deciding