The church had developed the doctrine that the Virgin Mary was, uniquely, conceived without original sin; this is known as the doctrine of the Immaculate Conception (which refers to the conception of Mary, not that of Jesus). In the Middle Ages the doctrine remained controversial, opposed by St Thomas Aquinas and his Dominican Order, but supported by Duns Scotus and his Franciscan Order. It was defined as dogma in 1854, by Pope Pius IX.[6]