sometimes called the Gnostic, a teacher of Gnosticism in the 2d century, thought by Jerome to be a native of Egypt; by Lardner, of Proconsular Asia; and by Neander, of Palestine. That Jerome's conjecture is correct, seems probable from the statement of Irenoeus that Marcus was a disciple of Valentinus. The followers of Marcus were called Marcosians. His peculiar tenets were founded on the Gnostic doctrine of aeons; professing to derive his knowledge of these aeons, and of the production of the universe, by a revelation from the four primal emanations in the system of aeons, who descended to .him from the region of the ineffable and invisible in the form of a female. He set forth his system in a poem, in which he introduced the divine aeon discoursing in liturgical forms, and with gorgeous symbols of worship. He prominently developed in his system the idea of a λόγος τοῦ ὄντος, of a word manifesting the hidden divine essence in the creation-creation being a continuous utterance or becoming expressed of the ineffable. See Irenaeus, Adv. Haeres. 1:8-18; Epiphanius, Haeres. 34, s. ut alii, 14; Tertullian, De Prescrip. liceret. c. 50 sq.; id. Adv. Valent. c. 4; id. De Resurrect. Carnsis, c. 5; Theodoret, Haereticarum Fabularum Compend. c. 9; Eusebius, I.E. 4:11; Philastrius, De lcaresib. post Christum, c. 14; Predestinatus, De Haeresib. 1:14; Augustin. De Iacres, c. 15; Jerome, Comm. ad Ist. 64:4, 5; Ep. ad Theod. 29; Ittigius, De Haeresiarchis, lect. ii, c. 6, § 4; Tillemont, Memoirs, 2:291; Lardner, Hist. of Heretics, book ii, e. 7; Neander, Hist. of the Christ. Ch. 1:440; Mosheim, Eccles. Hist. 1:147; Smith, Dict. of Greek and Roman Biog. and Mythol. s.v. (See MARCOSIANS); (See VALENTINIANS).