Byzantine scholar and statesman; b. Thessalonica, c. 1324; d. Crete, winter of 1397–98. As a student at the school of Nilus cabasilas, he joined the party of the future John VI Cantacuzenus who brought him to Constantinople; but after Cantacuzenus fell from power in 1354, Demetrius departed for Italy. In 1369 he became imperial secretary and accompanied John V Palaeologus to Rome; upon his return he lived privately until manuel ii palaeologus (1391–1425), his former pupil, had him return to court. He was in Venice with Manuel Chrysoloras (c. 1390), then in Milan and Crete. His epitaph was written by manuel calecas, who had been his disciple. Demetrius played an important role in politics, encouraging a Byzantine-Occidental alliance against the Turks. As friend of the humanists, he spread Oriental culture in the West and with his brother Prochorus cydones opposed Palamitism (see palamas, gregory). Before 1365 he was converted to Catholicism, and he translated Latin theological works into Greek, including writings of St. augustine, fulgentius of ruspe, St. Anselm of Canterbury, Ricoldo of Monte Croce, and the Summa contra Gentiles and the Summa theologiae (1a, 1a2ae, and 2a2ae) of St. Thomas Aquinas.
Bibliography: Works. Patrologia Graeca, ed. j. p. migne, 161 v. (Paris 1857–66), 109:637–652; 151:1283–1301; 154: 836–1212; Correspondance, ed. r. j. loenertz, 2 v. (Studi e Testi 186, 208; Rome 1956–60); Correspondance, ed. and tr. g. cammelli (Paris 1930). g. mercati, Notizie … Demetrio Cidone (Studi e Testi 56; Rome 1931). Literature. r. j. loenertz, Les Recueils de lettres de Démétrius Cydonès (Studi e Testi 131; Rome 1947). b. kotter, Lexikon für Theologie und Kirche, ed. j. hofer and k. rahner, 10 v. (2d, new ed. Frieburg 1957–65); suppl. Das Zweite Vatikanische Konzil: Dokumente und Kommentare, ed. h. s. brechter et al., pt. 1 (1966), 3:217. v. laurent, Dictionnaire d'histoire et de géographie ecclésiastiques, ed. a. baudrillart et al. (Paris 1912–), 14:205–208; "La Correspondance de Démétrius Cydonès," Échos d'Orient (Paris 1897–) 30 (1931) 339–354. m. calecas, Correspondance, ed. r. j. loenertz (Studi e Testi (Rome 152; (Rome 1950). c. buda, Byzantinische Zeitschrift 49 (1956), 318–331. Thomism. m. grabmann, "De rationibus fidei contra Saracenos … des hl. Thomas von Aquin," Scholastik 17 (1942) 187–216. h. g. beck, Kirche und theologische Literatur im byzantinischen Reich, (Munich 1959), 731–737.