Passage 10.23.8
ἀναλαβόντες οὖν τὰ ὅπλα καὶ διαστάντες ἔκτεινόν τε ἀλλήλους καὶ ἀνὰ μέρος ἐκτείνοντο, οὔτε γλώσσης τῆς ἐπιχωρίου συνιέντες οὔτε τὰς ἀλλήλων μορφὰς οὔτε τῶν θυρεῶν καθορῶντες τὰ σχήματα· ἀλλὰ ἀμφοτέραις ταῖς τάξεσιν ὁμοίως ὑπὸ τῆς ἐν τῷ παρόντι ἀγνοίας οἵ τε ἄνδρες οἱ ἀνθεστηκότες εἶναί σφισιν Ἕλληνες καὶ αὐτοὶ καὶ τὰ ὅπλα ἐφαίνοντο καὶ Ἑλλάδα ἀφιέναι τὴν φωνήν, ἥ τε ἐκ τοῦ θεοῦ μανία πλεῖστον ἐξειργάσατο ὑπʼ ἀλλήλων τοῖς Γαλάταις τὸν φόνον.
Then taking up their weapons and standing apart, they began slaying one another and being slain in turn, neither understanding the native tongue nor discerning each other's features nor recognizing the shapes of their shields. In both battle lines, due to their confusion at that moment, the warriors confronting them appeared similarly Greek, their arms appeared Greek, and their speech seemed to be Greek. Thus, the divine madness sent upon them brought about the greatest slaughter of the Gauls by one another.