LEONTIUS of Byzantium. — Antinomian theologian of the 6th century. Almost nothing is known of his life. He is not the same as the Scythian monk Leontius known from the theopaschite controversy; most probably, however, he is the same as the originist Leontius who is mentioned, as a Palestinian hermit, in the Life of St SABAS by CYRIL of Scitopolis (v. RICHARD, Léonce de Bysance était-il originiste?, in Revue des études byzantines, 5 [1947], pp. 31 ff). A skilful and learned polemicist, Aristotelian in logic and Neoplatonic in psychology, he sought to develop the theology of CYRILL of Alexandria using terms from the Council of Chalcedon.
His principal work is the three Books Adversus Nestorianos et Eutychianos (written c. 543-44; PG 86, 1, 1267-1396). Book I demonstrates the falsity of the premises underlying the theology of both Eutyches and Nestorius. Book II is a debate between an orthodox and an aphthartodocetist. Book III polemicises against THEODORE of Mopsuestia (v. R. DEVREESSE, Essai sur Théodore de Mopsuestie [Studi e testi, 141], Vatican City 1948, pp. 244 ff). L. also wrote two short treatises against SEVERUS of Antioch: one, Solutio argumentorum Severi (PG 68, 2, 1915-45), and Triginta capita adversus Nestorium (ibid. 1901-16; on these two works V. A. CASAMASSA, I tre libri di L. Bisanzio contro i nestoriani e i monofisiti, in Bessarione, 37 [1921], pp. 33-46). L. is not the author of the work De sectis (PG 86, 1, 1193-1268), which was probably written by THEODORE of Raithu; nor do the two works Adversus Nestorianos (ibid., 1399-1768) and Contra Monophysitas (ibid. 2, 1769-1901) come from L. of Byzantium, but from a Leontius of Jerusalem who took part in the Council of Constantinople (536). The short work Adversus fraudes Apollinaristarum, on the other hand, is probably to be attributed to L. of Byzantium. The first book became famous in theology for introducing the concept of enhypostasis into Christology.