Григорий XII
"Haec Sancta Synodus" marks the high-water mark of the Conciliar movement of reform. This decree, however, is not considered valid by the Magisterium of the Catholic Church, since it was never approved by Pope Gregory XII or his successors, and was passed by the council in a session before his confirmation. The church declared the first sessions of the Council of Constance an invalid and illicit assembly of bishops, gathered under the authority of John XXIII.