Which ecumenical council is credited with the doctrine on papal infallibility?

The First Vatican Council, also known as Vatican I, is credited with the doctrine of papal infallibility, which was formally defined in 1870. This council is significant in the history of the Catholic Church as it clarified the nature of the pope's authority in matters of faith and morals, asserting that when the pope speaks ex cathedra (from the chair of St. Peter), he is preserved from error in defining doctrines concerning faith or morals that the Church must hold.

This doctrine was a pivotal moment for the Catholic Church, reinforcing the centralized authority of the papacy during a time of considerable political and religious upheaval in Europe. The council aimed to address various challenges, particularly from rationalism and secularization, and the definition of papal infallibility was seen as a way to strengthen the Church’s authority.

In contrast, the other councils referenced either did not address the issue of papal infallibility directly or were focused on different theological disputes. The Council of Trent was primarily concerned with the Reformation and doctrinal affirmations in response to Protestant critiques. The Second Vatican Council introduced numerous reforms and emphasized engagement with the modern world but did not focus on papal infallibility. Nicaea I was mainly concerned with