Each suburbicarian diocese has a cardinal bishop at its titular head. On the same day Cardinal Giuliano della Rovere was named suburbicarian Bishop of Ostia. On 24 March 1884 he became Cardinal-Bishop of the suburbicarian diocese of Frascati. Six of the dioceses of the Roman Province are described as suburbicarian. In 883, John VIII's successor, Marinus I, restored Formosus to his suburbicarian diocese of Portus. On 13 March 1560 he was also created suburbicarian Bishop of Sabina. Pope Pius X's apostolic constitution "Apostolicae Romanorum" made this practice obligatory for all suburbicarian dioceses. He soon became a Cardinal-Bishop of the suburbicarian see of Frascati. In 1127 or 1128 Pope Honorius II promoted him to the suburbicarian See of Sabina. The University of Velletri established under the Suburbicarian see of Ostia. The Suburbicarian See of Velletri-Segni was created. He opted for the Suburbicarian Diocese of Frascati on 6 April 1620. On 27 September 1623 he opted for the Suburbicarian Diocese of Porto-Santa Rufina. In 1914, Velletri (now Velletri-Segni) was split off as a separate suburbicarian diocese.