Giovanni Maria Mastai-Ferretti, pope 1846–1878. The longest-serving pope in history. Initially seen as a liberal reformer, the 1848 revolutions transformed him into the arch-conservative who defined the modern papacy. He proclaimed the Immaculate Conception (1854), convened the First Vatican Council (1870) which defined papal infallibility, and issued the Syllabus of Errors (1864) condemning liberalism and modernism. He lost Rome to the Italian Kingdom in 1870.
- Lived: 1792 CE – 1878 CE
- Nationality: Italian
- Roles: Pope, Cleric
