The dogma of papal infallibility — defined at the First Vatican Council (1870 AD) — holds that when the Pope speaks ex cathedra (from the chair of Peter, formally defining doctrine on faith or morals to be held by the whole church), he is preserved from error by the Holy Spirit. Importantly, this is a much more limited claim than ‘the Pope is always right’ — ex cathedra definitions are rare (the most recent was the Assumption of Mary in 1950). The definition was controversial even within Catholicism at the time (the ‘minority’ at Vatican I that opposed it was significant). The Old Catholic Church separated from Rome partly in response to Vatican I. The dogma is a major obstacle in Catholic-Orthodox ecumenical dialogue, as Orthodox theology locates infallibility in the ecumenical council rather than in any single bishop, including Rome.