Kinlore
1869–1870 (Lateran Treaty 1929)

Vatican I, papal infallibility and the loss of Rome

The First Vatican Council defines papal infallibility just as Italian troops seize Rome, ending the pope's thousand-year rule over the Papal States.

  • Vatican I: The Council and the Making of the Ultramontane Church — John W. O'Malley, Harvard University Press (2018)
  • Saints and Sinners: A History of the Popes — Eamon Duffy, Yale University Press (2014)
  • Catechism of the Catholic Church (2nd edition) — Holy See, Libreria Editrice Vaticana (1997)

Well established politicsfaith

Part of the story of Catholicism and Italy.

Pope Pius IX, who had lost most of his territories to Italian unification, saw liberalism and nationalism as threats to the faith. The First Vatican Council, opened in December 1869, declared on 18 July 1870 that when the pope speaks ex cathedra, defining a doctrine of faith or morals for the whole church, he is preserved from error. Some bishops left Rome rather than vote against it, and a small group of dissenters formed the Old Catholic Church.

  • Vatican I: The Council and the Making of the Ultramontane Church — John W. O'Malley, Harvard University Press (2018)
  • Saints and Sinners: A History of the Popes — Eamon Duffy, Yale University Press (2014)
Two months later Italian troops entered Rome, and popes called themselves “prisoners in the Vatican” until the Lateran Treaty of 1929 created the independent Vatican City State. The only formal use of infallibility since 1870 was Pius XII’s definition of Mary’s Assumption into heaven in 1950.

Why it matters today

Catholicism

Infallibility is often misunderstood: it applies only to rare, solemn definitions of faith or morals, and has been formally used just once since 1870. But the council and the loss of the Papal States created the modern papacy, a spiritual authority with a tiny state, Vatican City, and a global voice.

Italy

For Italians, 20 September 1870, the breach of Rome's walls at Porta Pia, completed unification and made Rome the capital, but it opened a long rift between the new state and the Church. Popes told Catholics to stay out of national politics until the Lateran Treaty of 1929, signed with Mussolini, settled the "Roman question".