The moment
Pius IX opened the council on 8 December 1869 with about 700 bishops present. After months of argument, in which a minority held that a definition was inopportune, the constitution Pastor aeternus was adopted on 18 July 1870 with only two votes against, most of the minority having left Rome first. It declared that when the pope defines a doctrine of faith or morals ex cathedra he is infallible, and that such definitions are irreformable of themselves and 'not by the consent of the church'. Italian troops took Rome two months later and the council was suspended, never to be closed; Old Catholics broke away, and in Germany Bismarck's Kulturkampf against the Church followed.
People: Pius IX, Ignaz von Döllinger