Zacharias 18, nicknamed Kophos, was the metropolitan bishop of Chalcedon, appointed through the influence of Photios 1 (Ζαξηαρίου τοῦ Κωφοῦ, ὃς ὑπ' αὐτοῦ τῆς Χαλκηδόνος κεχειροτόνητο μητροπολίτης); in 867 he was sent by Photios 1 to Rome with Theodoros 175 (bishop of Laodikeia) with copies of the acts of the Council recently held under Photios 1 at Constantinople which deposed and excommunicated pope Nikolaos 28: Nicetas, Vita Ignatii 537C-D. Shortly afterwards the emperor Michael 11 was succeeded by Basil I (Basilios 7), and one of Basilios 7's first acts was to recall Zacharias 18 and his companions from their journey (τοὺς περὶ τὸν Ζαχαρίαν Καλχηδόνος ἐκ μέσης ἀπέστρεψε τῆς ὁδοῦ): Nicetas, Vita Ignatii 540A. He and Theodoros 175 were also given copies of a synodical letter by Photios 1 attacking Nikolaos 28, which they were to deliver, together with expensive gifts, to the king and queen of the Franks (Lodoïchos 1 and Engelberga 1), for them to expel Nikolaos 28 from his see: Nicetas, Vita Ignatii 541C. Possibly identical with Zacharias (τοῦ φαύλου Ζαχαρίου) who conveyed orders from the emperor Michael III (Michael 11) forbidding those who later consecrated Photios 1 from exercising any priestly functions: Theognostus, Libellus ad Nicolaum I 861A. This person does not appear to be the papal representative, Zacharias 19, but may be identical with the later partisan of Photios 1. Zacharias 18 was the metropolitan bishop of Chalkedon and the addressee of several letters from the patriarch Photius (Photios 1): Photius, Ep. 107 (addressed Ζαχαρίᾳ μητροπολίτῃ Χαλκηδόνος), Ep. 108 (addressed τῷ αὐτῷ) (both dateable between 870 and 873), Ep. 179 (date uncertain; addressed Ζαχαρίᾳ μητροπολίτῃ Χαλκηδόνος), Epp. 221, 223 (both dateable between 871 and 873, and addressed Ζαχαριᾳ μητροπολίτῃ Χαλκηδόνος). The letters are in Laourdas-Westerink I 147ff., II 68, 131-135. He was an old friend of Photios 1: Ep. 107, Ep. 221. He suffered from ill-health, Epp. 221, 223; and Photios 1 once sent him medicine for his stomach, Ep. 179. He is addressed as τέκνον ἡμέτερον ἐν κυρίῳ, and ἱερώτατε: Epp. 107, 108. Zacharias 18 was appointed bishop of Chalcedon by Photios 1 some time between 859 and 867; he took part in the Council of 869/870, at which he supported the Photian cause, and he was also present at the Council of 879/880; see Synodicum Vetus, 161. 7, p. 138; Mansi XVI 89-92, 98ff., 257A-C, 260E, XVIIA 373B; Theognostus, Libellus ad Nicolaum I 857CD, 861A.

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