Blessed Pope Pius IX (May 13, 1792 - February 7, 1878), born Giovanni Maria Mastai-Ferretti, was Pope from June 16, 1846, until 1878. His was the longest reign in Church History lasting almost 32 years. During his pontificate, he convened the First Vatican Council in 1869, which decreed Papal infallibility. The Pope defined the dogma of the Immaculate Conception of the Virgin Mary, meaning that Mary was conceived without original sin.