Pope Pius IX (; 13 May 1792 – 7 February 1878), born
Giovanni Maria Mastai-Ferretti, reigned from 16 June 1846 to his death in 1878. He was the
longest-reigning elected
pope in the history of the Catholic Church – over 31 years (the longest serving, un-elected pope was
Peter the Apostle, posthumously considered the first pope, who was confirmed by
Christ in 33 AD and killed by Emperor
Nero in 67 AD). During his pontificate, he convened the
First Vatican Council (1869–70), which decreed
papal infallibility, but the council was cut short due to the
loss of the Papal States.