Eutyches, an archimandrite at Constantinople, from whom the Eutychian controversy took its name. His christological views were an exaggeration of those of Cyril of Alexandria. He held that after the incarnation of Christ everything human in him had become merged in his divine essence, and that Christ therefore had but one nature. His personal enemies Domnus of Antioch and Eusebius of Dorylæum denounced him to Flavian, Archbishop of Constantinople, and at a synod held there in 448 A.D. he was condemned as a Valentinian and Apollinarian heretic. An œcumenical council was, through the influence at court of Dioscurus, Cyril's successor at Alexandria, called to Ephesus for a renewed investigation of the matter in dispute. Leo, Bishop of Rome, at the critical moment reversed the policy of the Roman see (his predecessor Celestine had favoured Cyril), and wrote to Flavian his famous epistle, in which he set forth authoritatively the doctrine of the two natures and one person. The council met at Ephesus in August 449, under the presidency of Dioscurus, and, under fear of the fists of his fanatical monks, decided everything exactly as he wished. Eutyches was restored, and Flavian, Eusebius of Dorylæum, Theodoret, and Domnus of Antioch were deposed. On the death of Theodosius II. the government passed into the hands of his sister Pulcheria and her husband Marcian (28th July 450). The fourth œcumenical council met at Chalcedon (q.v.), 8th October 451, and, though the greater number of the five or six hundred bishops shared the views of Dioscurus, the imperial authority insured the acceptance of the formula of Leo, and the resolutions passed in 449 by the 'Robber Council' (latrocinium Ephesinum)—the name given it by Leo—were annulled, as having been extorted by fear. Eutyches, who had previously been a second time excommunicated by Anatolius, Patriarch of Constantinople, was removed from the neighbourhood of the capital by Marcian before the meeting of the council. Afterwards, on the advice of Leo, he was transported to some remote place, but his subsequent history is unknown. The Eutychian sect was from 452 put down by penal laws.
For the later history of the opponents of the decrees of Chalcedon, see GREEK CHURCH. See also Mansi, Concilia, vols. v. vi. vii.; Hefele's Conciliengeschichte (2d ed. 1873 et seq.); Martin, Le Pseudo-Synode (1875); Perry, The Second Synod of Ephesus (1881); Amelini, S. Leone e l'Oriente (Rome, 1882); Krüger, Monophysitische Streitigkeiten (1884); Harnack, Dogmengeschichte, vol. ii. (1888).