MARIO MERCATORE. – Latin writer of the 5th century. According to E. Schwartz (*Acta Conc. Oec. I, 5, I* [1924], pp. 3-70), who identified his authentic works and reconstructed what can be known of his life, M. M. was African (St. Augustine, *Ep. 193*; PL 38, 869); in 418 he sent letters from Rome to St. Augustine against the Pelagians, which have since been lost; in 429 he was in Constantinople, where he engaged in translations and published treatises against the Pelagians and Nestorians; his traces are lost after the Council of Ephesus, which he certainly knew. M. M. had no original ideas; he was closely dependent on Cyril of Alexandria and Augustine. His polemic aimed chiefly at setting adversaries against one another, though rarely did he delve deeply into the issues. He was deeply concerned by the disputes disturbing the Churches of East and West, which explains his effort to link two such different heresies as Nestorianism and Pelagianism.
The works of M. M., preserved in a single manuscript (Palat. lat. 234 in the Vatican Library), are: *Marii Mercatoris servi Christi commonitorium lectori adversus haeresim Pelagii et Coelestii vel etiam scripta Iuliani* (this writing is later than 430, since it makes use of St. Augustine’s *Opus imperfectum contra Iulianum* [cf. E. Schwartz, op. cit., pp. 3-14]); *Refutatio symboli Mo- pussetani* (ibid., pp. 15-18); pamphlets against Nestorius and a translation of letters by Nestorius and Cyril of Alexandria (ibid., pp. 19-29; cf. p. XII and F. Loofs, *Nestoriana*, Halle 1905, pp. 103, 134-46); extracts of four anti-Pelagian sermons by Nestorius (E. Schwartz, op. cit., pp. 34-35); a letter of Nestorius and Caelestius (ibid., p. 35; cf. F. Loofs, op. cit., pp. 146-50); *Commonitorium super nomine Coelestii* (ibid., p. 36; a treatise addressed by M. M. in Greek to the Church of Constantinople and in Latin to Theodosius II; on the sources of this work cf. E. Schwartz, op. cit., p. X).
Here ends the corpus of M. M.’s works; the early editions mistakenly attribute to him the following translations: *Cyrilli et Nestorii XII capitula* (E. Schwartz, op. cit., p. 37); *Gesta Ephesiana* (minutes of the session of 22 July; ibid., p. 38); a defence of Cyril against the Antiochene party (ibid., p. 39); a defence of Cyril against Theodoret (ibid., p. 39); extracts from Theodoret, Theodore of Mopsuestia, Diodore of Tarsus, Ibas of Edessa and Eutherius of Thiana (ibid., pp. 41-54); later additions (ibid., pp. 55-57; cf. Bardenhewer, IV, p. 529).