Sedevacantism is a traditionalist Catholic movement which holds that since the 1958 death of Pius XII the occupiers of the Holy See are not valid popes due to their espousal of one or more heresies and that, for lack of a valid pope, the See of Rome is vacant. Sedevacantism owes its origins to the rejection of the theological and disciplinary changes implemented following the Second Vatican Council (1962–1965).