The First Vatican Council, convened by Pope Pius IX in 1869, was a significant ecumenical council of the Roman Catholic Church that addressed the challenges posed by modernity, including rationalism, liberalism, and materialism. It is most renowned for defining the dogma of papal infallibility, asserting that the Pope is preserved from the possibility of error when he solemnly declares a doctrine pertaining to faith or morals to be held by the whole Church.