Passage 10.20.9
ὁ δὲ ὡς κατὰ τὰς γεφύρας διεβίβασε τὴν στρατιάν, ἐχώρει πρὸς τὴν Ἡράκλειαν· καὶ διήρπασαν μὲν τὰ ἐκ τῆς χώρας οἱ Γαλάται καὶ ἀνθρώπους τοὺς ἐπὶ τῶν ἀγρῶν ἐγκαταληφθέντας ἐφόνευσαν, τὴν πόλιν δὲ οὐχ εἷλον. ἔτει γὰρ πρότερον τούτων οἱ Αἰτωλοὶ συντελεῖν τοὺς Ἡρακλεώτας ἠνάγκασαν ἐς τὸ Αἰτωλικόν· τότε οὖν ἠμύνοντο ὡς περὶ πόλεως οὐδέν τι Ἡρακλεώταις μᾶλλον ἢ καὶ αὑτοῖς προσηκούσης. ἦν δὲ καὶ τῷ Βρέννῳ τὰ μὲν Ἡρακλεωτῶν ἐλάσσονος φροντίδος, ἀγώνισμα δὲ ἐποιεῖτο ἐξελάσαι τε ἐκ τῶν στενῶν τοὺς ἀντικαθημένους καὶ παρελθεῖν ἐς τὴν ἐντὸς Θερμοπυλῶν Ἑλλάδα.
After he had led the army across by way of the bridges, he advanced toward Heracleia; the Gauls despoiled the countryside and slew the people left behind in the fields, but they did not take the city. A year before these events, the Aetolians had compelled the citizens of Heracleia to join the Aetolian League; thus now they defended Heracleia as though the city belonged not so much to the Heracleians as to themselves. Brennus, however, gave little thought to the affairs of Heracleia, but was eager above all to drive out those who guarded the pass and press forward into Greece beyond Thermopylae.