Theodoros 12 was patriarch of Jerusalem; at Pentecost (22 May), 763, he joined the patriarchs of Antioch and Alexandria, Theodoros 10 and Kosmas 3, and their bishops, in anathematising bishop Kosmas of Epiphaneia (Kosmas 4) for iconoclasm: Theoph. AM 6255 (ὃν κοινῇ γνώμῃ Θεόδωρος, ὁ πατριάρχης Ἀντιοχείας, καὶ Θεόδωρος Ἱεροσολύμων, καὶ Κοσμᾶς Ἀλεξανδρείας σὺν τοῖς ὑπ' αὐτοὺς ἐπισκόποις τῇ ἡμέρᾳ τῆς ἁγίας πεντηκοστῆς μετὰ τὴν ἀνάγνωσιν τοῦ ἁγίου εὐαγγελίου ὁμοφρόνως ἀνεθεμάτισαν ἕκαστος κατὰ τὴν ἑαυτοῦ πόλιν). He was patriarch of Jerusalem from 752/754 to at least 767; cf. Grumel, Chronologie, p. 451. Patriarch of Jerusalem; he was dead by 787; Theodoros 12, Kosmas 3 and Theodoros 10 received one another's synodika, and a copy of his was read out at the Second Council of Nikaia (the Seventh Ecumenical Council) at the third session (28 September 787), the text having been sent to the Council by the current eastern patriarchs: Mansi XII 1135 (Θεοδώρου τοῦ ἐν ἁγίας πατρὸς ἡμῶν καὶ πατριάρχου Ιεροσολύμων), cf. 1135-1146 (the synodika). He was the patriarch of Jerusalem who received the three-year old Michael Synkellos (Michael 51) and tonsured him and enrolled him among the readers of the Church of the Anastasis: Vita Mich. Sync. 2. The date was probably 764, when the patriarch was Theodoros 12. Later he sent him for instruction in grammar, rhetoric and philosophy: Vita Mich. Sync. 2.

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