Marcus Diadochus (Markos o diadochos), an obscure writer of the fourth century of whom nothing is known but his name at the head of a “Sermon against the Arians”, discovered by Wetsten in a manuscript codex of St. Athanasius at Basle and published by him at the end of his edition of Origen: “De oratione” (Basle, 1694). Another version of the same work was lent by Galliciollus to Galland and published in the “Veterum Patrum Bibliotheca”, V (Venice, 1765-1781). This is the text in P.G., LXV, 1149-1166. The sermon quotes arid expounds the usual texts, John, i, 1; Heb., i, 3; Ps. cix, 3-4; John, xiv, 6, 23, etc., and answers difficulties from Mark, xiii, 32; x, 10; Matt., xx, 23, etc.
A quite different person is Diadochus, Bishop of Photike in Epirus in the fifth century, author of a “Sermon on the Ascension” and of a hundred “Chapters on Spiritual Perfection” (P.G., LXV, 1141-1148, 1167-1212), whom Victor Vitensis praises in the prologue of his history of the Vandal persecution (Ruinart’s edition, Paris, 1694, not. 3). The two are often confounded, as in Migne.