Catholic Encyclopedia (1913)/Petrus Diaconus
The name of several men of note in ecclesiastical history and literature.
(1) One of the Scythian monks who appeared in 519 before Pope Hormisdas in connexion with the Theopaschite controversy. He wrote concerning this question his treatise "De incarnatione et gratia", at the same time directed against the teaching of Faustus of Riez respecting grace and addressed to St. Fulgentius of Ruspe; in P. L., LXII, 83-92; Bardenhewer, tr. Shahan, "Patrology", 548, 1908 (St. Louis).
(2) A disciple and friend of Gregory the Great; d. at Rome 12 March, 605 or 606. His questioning occasioned the composition of Gregory's "Dialogues". He is also authority for the statement that the Holy Spirit sometimes hovered in the form of a dove over the great pope's head.
(3) A monk of Monte Cassino known also as Petrus Subdiaconus; d. c. 960. He was subdeacon of the church of St. Januarius at Naples, and he continued the history of this diocese (Gesta episc. Neap.), an anonymous work which had already been added to by John the Deacon. He wrote the lives of several saints, including, according to some critics, that of Athanasius, Bishop of Naples ("Vita et translatio Athanasii ep. Neap.").
(4) Another monk of Monte Cassino, also called "the Librarian" (Bibliothecarius), b. c. 1107 at Rome; d. probably c. 1140. A descendant of the Counts of Tusculum, he was offered in 1115 to the monastery of Monte Cassino. About 1127 he was forced to leave the abbey and retired to the neighbouring Atina, seemingly because he was an adherent of the Abbot Orderisius. In 1137 he was allowed to return to Monte Cassino. That same year he appeared before Emperor Lothair II, then in Italy, on behalf of his monastery. The sovereign was so pleased with him that he appointed him his chaplain and secretary, and would probably have attached him permanently to his person had not Abbot Wibald considered Peter's return necessary to the abbey. At Monte Cassino Peter became librarian and keeper of the archives, of which he compiled a register. Besides continuing the chronicle of Monte Cassino by Leo Marsicanus (or Ostiensis) from 1075 to 1138, he wrote several historical works: "De viris illustribus Casinensibus"; "De ortu et obitu justorum Casinensium"; "De Locis sanctis"; Disciplina Casinensis"; "Rhythmus de novissimis diebus". Peter forged, under the name of Gordian, the Passion of St. Placidus. He is vain and occasionally untruthful, but an entertaining writer. His works are in P. L., CLXXIII, 763-1144.
(2) Acta SS., March, II, 208-9; MANN, Lives of the Popes, I (St. Louis, 1902), i, 243-44. (4) P. L., CLXXIII, 462-80; BALZANI, Early Chroniclers of Europe, Italy (London, 1883), 174-80; MANN, Lives of the Popes, VII (St. Louis, 1910), 218.