Passage 9.16.6
πρὸς δὲ ταῖς καλουμέναις πύλαις Προιτίσι θέατρον ᾠκοδόμηται, καὶ ἐγγυτάτω τοῦ θεάτρου Διονύσου ναός ἐστιν ἐπίκλησιν Λυσίου· Θηβαίων γὰρ αἰχμαλώτους ἄνδρας ἐχομένους ὑπὸ Θρᾳκῶν, ὡς ἀγόμενοι κατὰ τὴν Ἁλιαρτίαν ἐγίνοντο, ἔλυσεν ὁ θεὸς καὶ ἀποκτεῖναί σφισι τοὺς Θρᾷκας παρέδωκεν ὑπνωμένους. ἐνταῦθα οἱ Θηβαῖοι τὸ ἕτερον τῶν ἀγαλμάτων φασὶν εἶναι Σεμέλης· ἐνιαυτοῦ δὲ ἅπαξ ἑκάστου τὸ ἱερὸν ἀνοιγνύναι φασὶν ἐν ἡμέραις τακταῖς.
Near the gates known as the Proetidian, a theatre has been built, and very close to this theatre stands a temple dedicated to Dionysus, surnamed Lysius ("the Deliverer"). For the god delivered certain Theban men who had been taken prisoner by Thracians; as they were passing through the lands of Haliartus, the god freed them and delivered over to them the Thracians whom they slew as they lay asleep. The Thebans assert that one of the statues here represents Semele, and say that this sanctuary is opened only once each year, upon fixed days.