Ioannes 52 was bishop of Hadrianoi in Bithynia (one text, see below, says Hellespontos); in 681 he attended the Third Council of Constantinople (the Sixth Ecumenical Council) and was present at two of the last three sessions (sessions sixteen and eighteen, on 9 August and 16 September): Riedinger II 2. 690-790 (= Mansi XI 616-650). In the subscriptions to the statement of the faith, which condemned monotheletism, he is styled Ἰωάννης ἐλέει Θεοῦ ἐπίσκοπος τῆς Ἁδριανῶν πόλεως τῆς Ἑλλησποντίων ἐπαρχίας: Riedinger II 2. 790, line 16 (= Mansi XI 649). The old Latin version of this printed in Riedinger II 2. 791, line 19 (= Mansi XI 650), calls him "episcopus Adrianupoleos Bitiniae regionis". His name does not appear among the signatures to the Council (Riedinger II 2. 822-829 (= Mansi XI 668-681)). In the lists of those present at each session he is styled Ἰωάννου ἐπισκόπου Ἀδριανῶν (the Mansi version at XI 628 adds the word Βιθινίας): Riedinger II 2. 690, line 6, 760, line 14 (= Mansi XI 616, 628).

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