Catholic Encyclopedia (1913)/Marcus Diadochus
Marcus Diadochus (Μάρκος ὁ διάδοχος), 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 and 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.
P. G. LXV, 1141-1212; Jungmann-Fessler, Institutiones Patrologiæ (Innsbruck, 1896), IIb, 147-148; Chevalier, Bio-Bibl., s.v.