The First Vatican Council, held in St. Peter's Basilica in Rome from 1869 to 1870, was initiated by Pope Pius IX to address contemporary issues of the Church and modern society. One of the key outcomes of this council was the definitive affirmation of the dogma of papal infallibility. This doctrine specifies that the Pope, when speaking ex cathedra, or 'from the chair' of Saint Peter, is preserved from error in defining doctrines related to faith and morals. The council’s leaders, including prominent bishops and theologians, debated the implications of this declaration vigorously, as it posed significant ramifications for the governance of the Catholic Church. During the fourth session on July 18, 1870, a decisive vote led to the formal declaration of the doctrine with 533 votes in favor and merely 2 against, highlighting the strong consensus among the bishops. The ruling was viewed as crucial for asserting the Pope's authority, particularly in the face of rising skepticism towards organized religion and numerous challenges from modern philosophies and socio-political movements. The declaration led to an affirmation of the Pope’s supreme authority and played a pivotal role in the Catholic Church’s response to rapid modernization and secular influences in the 19th century. The backdrop of the council included the unification of Italy and the diminishing temporal power of the Papacy, spurring a need for papal centrality in doctrinal matters. The Council of Trent had already established foundational religious principles; however, the declaration of papal infallibility brought a new level of doctrinal clarity and assertiveness amid growing tensions in Europe, particularly from rationalist thought and revolutionary movements. This momentous decision is considered a touchstone in Catholic dogmatic theology, solidifying the Pope's role both as a spiritual leader and as a point of unity for the universal Church.