Marius Mercator, ecclesiastical writer, b. probably in Northern Africa about 390; d. shortly after 451. In 417 or 418 he was in Rome where he wrote two anti-Pelagian treatises, which he submitted to St. Augustine (Ep. ad M. M., no. 193). From 429 till about 448 he was in Constantinople. His works, mostly translations and compilations of excerpts from heretical as well as orthodox Greek theological writers, were edited by Garnier (Paris, 1673), reprinted in Migne (P.L., XLVIII, Paris, 1846). They were also edited by Baluze (Paris, 1684), reprinted with corrections in Galland, “Bibliotheca veterum Patrum”, VIII (Venice, 1772), 613-738. His treatises “Commonitorium super nomine Caelestii”, and “Commonitorium adversus haeresim Pelagii et Caelestii vel etiam scripta Juliani” are against the Pelagians. The former (in Migne, loc. cit., 63-108) effected the expulsion of Julian of Eclanum and Caelestius from Constantinople and their condemnation at Ephesus in 431. The latter is in Migne, loc. cit., 109-172. Against the Nestorians he wrote “Epistola de discrimine inter haeresim Nestorii et dogmata Pauli Samosateni, Ebionis, Photini atque Marcelli” (Migne, loc. cit., 773) and “Nestorii blasphemiarum capitula XII” (Migne, loc. cit., 907-932). Among his translations are extracts from Cyril of Alexandria, Nestorius, Theodore of Mopsuestia, Theodoret, Pelagius, and others.