Read right under “Papal Infallibility”
Pope Pius, in 1854, used the doctrine of papal infallibility to define as dogma the Immaculate Conception of Mary...
It was part of the Wiki article, and so I thought I would include it as a question -— because Pope Pius (in 1854) used the doctrine of papal infallibility to define as dogma the Immaculate Conception of Mary.
Ok.