Theophylaktos 57 was the author of the Life of St Theophylact archbishop of Nikomedeia (Theophylaktos 37): Vita S. Theophylacti. His name is inferred from chapter 19 of the Life where he says that it was synonymous with that of his subject. The work was clearly composed by a person living in Nikomedeia but some time after the death of Theophylaktos (chapter 8 mentions Theophylaktos 37's building works ἐν ταύτῃ τῇ πόλει and alludes to the bishops who had succeeded Theophylaktos 37 in the see). Theophylaktos 57 was probably a cleric there, living around the middle of the ninth century; cf. Vita S. Theophylacti, ed. Vogt, introduction, pp. 68ff.

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