Passage 9.12.3
φασὶ δὲ οἱ Θηβαῖοι, καθότι τῆς ἀκροπόλεως ἀγορά σφισιν ἐφʼ ἡμῶν πεποίηται, Κάδμου τὸ ἀρχαῖον οἰκίαν εἶναι· θαλάμων δὲ ἀποφαίνουσι τοῦ μὲν Ἁρμονίας ἐρείπια καὶ ὃν Σεμέλης φασὶν εἶναι, τοῦτον δὲ καὶ ἐς ἡμᾶς ἔτι ἄβατον φυλάσσουσιν ἀνθρώποις. Ἑλλήνων δὲ τοῖς ἀποδεχομένοις ᾆσαι Μούσας ἐς τὸν Ἁρμονίας γάμον τὸ χωρίον ἐστὶν ἐπὶ τῆς ἀγορᾶς, ἔνθα δή φασι τὰς θεὰς ᾆσαι.
The Thebans say that the place which in our day serves as their market-place, below the acropolis, was originally the dwelling of Cadmus. They still point out among the ruins certain chambers, one said to have belonged to Harmonia, and another claimed to be Semele's, the latter continuing even to our day to be guarded and kept inaccessible to human beings. Within the market-place itself there is also the spot where, according to those Greeks who hold that the Muses sang at the wedding of Harmonia, these goddesses performed their chants.