Antonios 3 was nicknamed Bursodepses (the Tanner): Nicetas, Vita Ignatii 493C (cited below).

Son of a priest who was also (or had been) a cobbler (Anonymus 29), Antonios 3 was originally called Konstantinos Kasymatas (Κωνσταντῖνον, υἱὸν πρεσβυτέρου τινὸς τζαγγαρίου, καὶ Κασυματᾶ); he studied grammar and became a teacher of law (γέροντα νομικὸν, rightly corrected to γεγονότα; see R. Browning, "Notes on the Scriptor Incertus de Leone Armenio", in Byz. 35 (1965), p. 394, P. Lemerle, Byzantine Humanism: The First Phase (Canberra, 1986), p. 161, n. 132; on nomikos, here perhaps a teacher of law rather than a notary (because it was a teaching post - διδάξαντα παιδία), cf. Lemerle, op. cit., p. 162, n. 133; see however Browning, op. cit., p. 404, a notary who also taught young children) in the district of Ta Sphorakiou at Constantinople; when (unspecified) charges were brought against him (δι' ἐγκλήματά τινα), he fled to a monastery and received the tonsure, adopting the monastic name Antonios; subsequently he became head (ἡγούμενος) of the monastery of Ta Metropoliton; later still he became bishop of Syllaion; originally he supported the veneration of icons but later changed, allegedly for opportunistic reasons, and became an iconoclast; in 814 he was summoned to become a member of the commission set up at Constantinople by the emperor Leo V (Leo 15) under Ioannes 5 (John the Grammarian, the future patriarch) to examine theological literature for texts to support the iconoclast position; they needed someone of episcopal status and the name of Antonios was proposed by Ioannes 5 and the others to the emperor: Scriptor Incertus 350-352. He became the head of the commission (ἄγεται ἀρχηγὸς καὶ πρῶτος αὐτῶν), taking up his post in July 814: Scriptor Incertus 352. An allusion to his father's trade and a description of Antonios as a teller of trivial tales and jokes, who encouraged his monks to copy his example and who generally lived an unworthy life (Scriptor Incertus 351) form part of the hostile iconophile tradition. In December 814 the commission members produced the texts they had found and openly began to challenge the patriarch Nikephoros 2 and the iconophiles: Scriptor Incertus 352-356 (the name of Antonios always appears first in references to the commission, e.g. 353 τοὺς περὶ Ἀντώνιον καὶ Ἰωάννην).

In the Life of Niketas of Medikion, Antonios 3 is named among the bishops who worked with the emperor Leo V (Leo 15) against the veneration of icons: Vita Nicetae Medicii 31 (εἶχεν μὲν συνεργοὺς ἐκ μὲν τῶν ὑπὸ θρόνον Ἀντώνιον τὸν τοῦ Συλαίου).

Bishop of Syllaion: Nic., Chron. 80, cf. Ps.-Symeon 621 (cited below) (but cf. below, for Perge).

Antonios 3 became patriarch of Constantinople (πατριαρχῆσαι Κωνσταντινουπόλεως) in succession to Theodotos 2 in 821 and held office for sixteen years (so a scholion interpolated into the text of Theophanes; Nic., Chron. gives twelve years): Nic. Chron. 80, Theoph. AM 6177, Zon. XV 24. 14 (Ἀντώνιος προεχειρίσθη, ᾧ Κασσυματᾶς τὸ ἐπώνυμον). His dates were 821 to 837. Formerly bishop of Syllaion, he was patriarch of Constantinople during the reign of the emperor Michael II (Michael 10): Ps.-Symeon 621 (called Ἀντώνιος ὁ τοῦ Συλαίου). According to the Life of Ignatios by Nicetas, he became metropolitan bishop of Perge (i.e. Syllaion, in Pamphylia) and was an active spokesman against the veneration of icons; therefore, at the death of the patriarch Theodotos Kassiteras (Theodotos 2) (in 821), he was appointed by the emperor Michael II (Michael 10) to succeed Theodotos as patriarch of Constantinople: Nicetas, Vita Ignatii 493C (τὸν Βυρσοδέψην καλούμενον Ἀντώνιον, μητροπολίτην μὲν ἤδη Πέργης γενόμενον καὶ τῆς αἱρέσεως κοινωνόν, σχολάζοντα δέ, ὁ αὐτὸς Μιχαὴλ ἀναλαβών, ἀρχιερέα Κωνσταντινουπόλεως ἀποδείκνυσι). He opposed the veneration of icons (τῆς προσκυνησέως τῶν ἁγίων εἰκόνων ἀλλότριος): Ps.-Symeon 621, cf. Zon. XV 24. 14.

Antonios 3 is mentioned but not named in two of the letters of Theodoros 15 (Theodore the Stoudite): Theod. Stud., Ep. 469, pp. 672-674 (letter to the patriarch of Jerusalem, Thomas 60, written between 821 and 826, mentions (p. 672, lines 9-11) τοῦ θεσπεσιωτάτου ἡμῶν ἀρχιποίμενος, ἐφ' ᾧ πᾶς καὶ παντὸς ὁ τῆς εὐφημίας εἰκότως ἀνάπτοιτο λόγος), Ep. 471, pp. 676-678 (to Gregorios 139, between 821 and 825, mentions (p. 678, line 47) ὁ ἱερώτατος ἡμῶν πατριάρχης). Presumably in late 829, he crowned the new emperor Theophilos (Theophilos 5) and at Pentecost (5 June 830), together with the other clergy and the senate, he received a large donation from the emperor: Leo Gramm. 213-214, Ps.-Symeon 625, Georg. Mon. Cont. 790.

One of his relations (Anonymus 34) served under the emperor Theophilos (Theophilos 5) as archon of the chrysochoon: Leo Gramm. 215 (συγγενοῦς Ἀντωνίου πατριάρχου), Georg. Mon. Cont. 793.

Antonios 3 died in office (in 837) and was succeeded by Ioannes 5: Leo Gramm. 221, Georg. Mon. Cont. 799, Ps.-Symeon 635, Zon. XV 28. 32 (after thirteen years (sic)), Nicetas, Vita Ignatii 493D.

One of his seals survives: Laurent, Corpus V 1, 4 = Zacos and Veglery 1417 = Zacos II, no. 3 = Oikonomides, Dated Seals, p. 54, no. 45. Obv.: cruciform monogram of Κύριε βοήθει. Rev.: Αντω - νιω επις - κοπω Κων - σταντινου - [πο]λε[ωσ]. On the identification of the owner, see Oikonomides, op. cit., p. 54.

Antonios 3 is one of the leading iconoclasts anathematised in the Synodikon of Orthodoxy (τοῖς ἀλληλοπροξένοις τῶν κάκων καὶ ἑτεροδιαδόχοις τὴν δυσσεβείαν; see also Theodotos 2 and Ioannes 5): Gouillard, "Synodikon", p. 57, lines 173-174. He was anathematised as an iconoclast in a passage which was interpolated into the proceedings of the Second Council of Nikaia (the Seventh Ecumenical Council): Mansi XIII 400. See further Theodoros 66. The date of the anathemas may have been the Triumph of Orthodoxy in 843.

On Antonios 3, see also Catal. Patr. p. 291, line 24, and cf. ODB I 124, P. J. Alexander, The Patriarch Nicephorus of Constantinople (Oxford, 1958), p. 281, J. Gouillard, "Une oeuvre inédite du patriarche Méthode: la Vie d'Euthyme de Sardes", BZ 53 (1960), p. 43, Grumel, Regestes II 412 and id., Chronologie, p. 435 (c. January 821-January 837, before 21 January).

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