Pius IX

Catholic devotion to the idea that Mary was conceived without the stain of original sin had circulated for centuries before Pius IX, argued over by theologians and celebrated in popular feast days without ever being formally defined as required belief. In 1854, after consulting the bishops of the world by letter and receiving overwhelming support, Pius IX issued the bull Ineffabilis Deus, declaring the Immaculate Conception a dogma that all Catholics were bound to hold, using his authority as pope to settle a question theologians had debated since the Middle Ages without waiting for a council to do so.

The declaration mattered beyond its specific content because of how it was made. Pius IX did not summon bishops to debate and vote on the question in the manner of the ancient councils; he consulted them individually and then proclaimed the doctrine himself, treating papal authority as sufficient on its own to settle a matter of faith. This method anticipated, and to some historians directly prepared the ground for, the doctrine of papal infallibility that the First Vatican Council would formally define sixteen years later, since Pius had, in practice, already exercised the kind of authority infallibility would describe.

The dogma also connected directly to a wave of Marian apparitions reported during his pontificate, most famously at Lourdes in 1858, only four years after Ineffabilis Deus, where the visionary Bernadette Soubirous reported the figure identifying herself using words Bernadette, untrained in theology, would not otherwise have known, I am the Immaculate Conception, a detail widely read at the time as confirming the pope's recent definition from outside the church's own hierarchy.

Pius IX convened the First Vatican Council in December 1869, the first general council of the church in over three hundred years, gathering more than seven hundred bishops from across the world. Its central and most contested achievement was the dogmatic constitution Pastor Aeternus, defining that the pope, when speaking ex cathedra on a matter of faith or morals in his capacity as shepherd of the whole church, possesses the infallibility Christ willed his church to enjoy, a definition passed after real debate and open opposition from a minority of bishops who feared it overstated papal authority against that of bishops and councils.

The council never finished its planned agenda. In July 1870, the Kingdom of Italy, which had already absorbed most of the former Papal States over the preceding decade, took advantage of France's withdrawal of its protective garrison during the Franco-Prussian War to send troops into Rome itself. After a brief token resistance, the city fell in September 1870, and Pius IX suspended the council indefinitely rather than close it, a suspension that in practice lasted almost ninety years until the Second Vatican Council reopened the conversation the First had left unfinished.

Pius IX responded to the loss of Rome by refusing to recognize Italian sovereignty over the city or to leave the Vatican grounds, declaring himself a prisoner of the Vatican, a self-imposed confinement his three immediate successors maintained, and which was not resolved until the Lateran Treaty of 1929 created the independent Vatican City state under a later pope. Pius IX himself never saw the standoff end, dying in 1878 still formally unreconciled with the kingdom that had taken his temporal domain.