Sisinnios 18 was bishop of Hadrianeia in Hellespontus; in 787 he attended the Second Council of Nikaia (the Seventh Ecumenical Council) and was apparently present at all sessions except the first, from 26 September to 23 November 787: Mansi XII 1099-XIII 486. He is not attested in the list of those present at the first session. In the list of those present at the seventh session he is styled Σισιννίου ἐπισκόπου Ἀδρανίας: Mansi XIII 368. Elsewhere he is styled Σισίννιος ὁ ὁσιώτατος ἐπίσκοπος Ἀδρανείας or similar: Mansi XII 1099 (in the Latin version, at XII 1100, his name is given as "Ioannes"), XIII 144 (Ἀδρανίας), XIII 389. At the second session he supported the traditional veneration of icons as described in statements from pope Hadrian I (Hadrianos 1) and condemned iconoclasts: Mansi XII 1099. At the fourth session he subscribed the statements read out from the Fathers in support of the veneration of icons: Mansi XIII 144. At the seventh session he subscribed the statement of the faith adopted by the Council: Mansi XIII 389.

(Publishable link for this person: )