Passage 10.21.1
προελθὼν οὖν ἀπὸ τῆς Ἡρακλείας---ἐπυνθάνετο γὰρ παρὰ αὐτομόλων τοὺς συνειλεγμένους ἐς Πύλας ἀπὸ ἑκάστης πόλεως--- ὑπερεφρόνει τε τοῦ Ἑλληνικοῦ καὶ ἦρχεν ἐς τὴν ἐπιοῦσαν μάχης ἅμα ἀνίσχοντι τῷ ἡλίῳ, οὔτε Ἕλληνα ἔχων μάντιν οὔτε ἱεροῖς ἐπιχωρίοις χρώμενος, εἰ δὴ ἔστι γε μαντεία Κελτική. ἐνταῦθα οἱ Ἕλληνες ἐν σιγῇ τε ἐπῄεσαν καὶ ἐν κόσμῳ· καὶ ὡς ἀφίκοντο ἐς χεῖρας, οὔτε σφίσιν οἱ πεζοὶ τοσοῦτο ἀπὸ τῆς τάξεως ἐξέθεον ὥστε τὴν φάλαγγα ἐπιταράσσειν τὴν οἰκείαν καὶ οἱ ψιλοὶ μένοντες κατὰ χώραν τά τε ἀκόντια ἔπεμπον καὶ ὅσα ἀπὸ τῶν τόξων ἢ σφενδονῶν.
After advancing from Heracleia—for he had been informed by deserters about the contingents gathered at Thermopylae from each city—he treated the Greek force with contempt and began preparations for battle at sunrise the next day. He had neither a Greek diviner nor did he conduct rites according to local custom, if indeed a Celtic divination exists at all. Here the Greeks advanced silently and in good order. Once they engaged, their infantry did not rush forward from the line far enough to disrupt their own phalanx, and the light-armed troops kept their positions, sending forth javelins and whatever missiles they had from their bows or slings.