GREGORIO MAMMAS. - Catholic Patriarch of Constantinople, successor of Metrofane (d. 1443), likewise a Catholic. In 1451 he was obliged to take refuge in Rome, where he died in 1459. G. took part in the Council of Florence in the years 1438–39 as vicar of the Greek Patriarch of Alexandria, protesyncellus of the Patriarch of Constantinople, and confessor to the Byzantine Emperor Giovanni VIII, who was present at that assembly. He subscribed to the Bull of Union of 6 July 1439 and always remained faithful to the unity of the Roman Church; indeed, he became its defender through his two apologetic treatises directed against his bitter adversary Marco Eugenico and through a theological work addressed to the Emperor of Trebizond in defence of Catholic doctrine.
These three works have already been published, whereas another three, of which he himself speaks (PG 160, 198 C), are still unpublished; these too deal with the articles of faith defined in the Bull of Union of the Greeks. G. M., of noble character, was greatly esteemed by Popes Eugenio IV, Nicola V, Callisto III, and Pio II. The latter wrote of him that he had died “not without the reputation of sanctity.” His funerary inscription is known, but unfortunately his tomb, probably at S. Giorgio in Velabro in Rome, has not yet been discovered.