Sisinnios 15 was bishop of Parion (in Hellespontus); in 787 he attended the Second Council of Nikaia (the Seventh Ecumenical Council) and was probably present at all eight sessions, from 24 September to 23 November 787: Mansi XII 994-XIII 486. In the lists of those present at the first and seventh sessions he is styled Σισιννίου ἐπισκόπου τοῦ Παρίου: Mansi XII 994, XIII 368. Elsewhere he is styled Σισίννιος ὁ ὁσιώτατος ἐπίσκοπος Παρίου or similar: Mansi XII 1095, XIII 140, XIII 384 (τοῦ Παρίου). At the second session he spoke in support of the traditional veneration of icons as described in statements from pope Hadrian I (Hadrianos 1) and condemned iconoclasts: Mansi XII 1095. At the fourth session he subscribed to the statements read out from the Fathers in support of the veneration of icons: Mansi XIII 140. At the seventh session he subscribed the statement of the faith adopted by the Council: Mansi XIII 384.

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