Passage 9.5.7
μαρτυρεῖ δέ μοι τῷ λόγῳ καὶ Ὅμηρος ἐν τῇ Ὀδυσσείᾳ· οἳ πρῶτοι Θήβης ἕδος ἔκτισαν ἑπταπύλοιο πύργωσάν τʼ, ἐπεὶ οὐ μὲν ἀπύργωτόν γʼ ἐδύναντο ναιέμεν εὐρύχορον Θήβην, κρατερώ περ ἐόντε. Hom. Od. 11.263 ὅτι δὲ Ἀμφίων ᾖδε καὶ τὸ τεῖχος ἐξειργάζετο πρὸς τὴν λύραν, οὐδένα ἐποιήσατο λόγον ἐν τοῖς ἔπεσι· δόξαν δὲ ἔσχεν Ἀμφίων ἐπὶ μουσικῇ, τήν τε ἁρμονίαν τὴν Λυδῶν κατὰ κῆδος τὸ Ταντάλου παρʼ αὐτῶν μαθὼν καὶ χορδὰς ἐπὶ τέσσαρσι ταῖς πρότερον τρεῖς ἀνευρών.
Homer in the Odyssey also supports my account, saying: "Those who first built the seat of seven-gated Thebes, and fortified it—for although they were strong, they could not inhabit broad-streeted Thebes without walls." But that Amphion sang and constructed the wall to the accompaniment of his lyre, Homer made no mention in his poetry. Amphion, however, acquired great fame for music, having learned from the Lydians, through his kinship with Tantalus, the harmony named after them, and having added a fourth string to the previous three.