Arsenios 5 was a monk of the monastery of Medikion, he is mentioned in three letters from Theodoros 15 (Theodore the Stoudite) written in 816, 818 and 821 to the hegoumenos of Medikion, Niketas 43, in which Theodoros 15 sent greetings to him: Theod. Stud., Ep. 255 (M/L 816; τὸν ἀληθῶς Ἀρσένιον, τὸν ἄρσενα τῇ φρονήσει καὶ διάπυρον τῷ ζήλῳ, τὸν σὸν μὲν ἀληθινὸν υἱόν, ἐμὸν δὲ ἐραστὸν ἀδελφόν), Ep. 319 (March/April 818; ἀδελφόν), Ep. 422 (E 821; one of the ἀδελφοί, he was τὸν ἱερὸν Ἀρσένιον). Arsenios 5 wrote to Theodoros 15 in 816/817 about the defection of Niketas 43 and received a letter in reply rejoicing at Niketas 43's repentance: Theod. Stud., Ep. 281 (L 816/E 817; addressed Ἀρσενίῳ μοναχῷ). To judge by the dates, he was with Niketas 43 during the latter's exile on Prokonnesos and Hagia Glykeria.

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