Sisinnios 23 was bishop of Chersonesos in Crete; in 787 he attended the Second Council of Nikaia (the Seventh Ecumenical Council) and is attested at the fourth and seventh sessions, on 1 October and 13 October 787; he probably attended the last five sessions: Mansi XIII 145-486. In th list of those present at the seventh session he is styled Σισιννίου ἐπισκόπου Χερσονήσου: Mansi XIII 369. Elsewhere he is styled Σισίννιος ἐπίσκοπος Χερσονήσου or similar: Mansi XIII 145, XIII 392. At the fourth session he subscribed the statements read out from the Fathers in support of the veneration of icons: Mansi XIII 145. At the seventh session he subscribed the statement of the faith adopted by the Council: Mansi XIII 392.

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