Fulgens Corona §1

¹ The radiant crown of glory with which the most pure brow of the Virgin Mother was encircled by God, seems to Us to shine more brilliantly, as We recall to mind the day, on which, one hundred years ago, Our Predecessor of happy memory Pius IX, surrounded by a vast retinue of Cardinals and Bishops, with infallible apostolic authority defined, pronounced and solemnly sanctioned "that the doctrine, which holds that the Most Blessed Virgin Mary at the first moment of her conception was, by singular grace and privilege of the Omnipotent God, in virtue of the merits of Jesus Christ, Savior of the Human race, preserved from all stains of original sin, is revealed by God, and therefore to be firmly and resolutely believed by all the faithful." (Dogmatic bull Ineffabilis Deus , of Dec. 8, 1854.)