Passage 3.4.8
Ξέρξῃ γὰρ βασιλέων, ὁπόσοι Μήδοις καὶ Πέρσαις ἐγένοντο ὕστερον, παρασχομένῳ μέγιστον φρόνημα καὶ ἀποδειξαμένῳ λαμπρὰ οὕτω, κατὰ τὴν πορείαν Λεωνίδας σὺν ὀλίγοις, οὓς ἠγάγετο ἐς Θερμοπύλας, ἐγένετο ἂν ἐμποδὼν μηδὲ ἀρχὴν τὴν Ἑλλάδα ἰδεῖν αὐτὸν μηδὲ Ἀθηναίων ποτὲ ἐμπρῆσαι τὴν πόλιν, εἰ μὴ κατὰ τὴν ἀτραπὸν τὴν διὰ τῆς Οἴτης τείνουσαν περιαγαγὼν τὴν μετὰ Ὑδάρνου στρατιὰν ὁ Τραχίνιος κυκλώσασθαί σφισι τοὺς Ἕλληνας παρέσχε καὶ οὕτω κατεργασθέντος Λεωνίδου παρῆλθον ἐς τὴν Ἑλλάδα οἱ βάρβαροι.
For Xerxes, whose pride exceeded that of all kings who subsequently ruled the Medes and the Persians, and whose exploits displayed such remarkable brilliance, Leonidas, with the small band he led to Thermopylae, would have effectively barred his march, preventing him from even seeing Greece at all or ever setting fire to the city of the Athenians—if only the Trachinian had not guided the troops led by Hydarnes along the narrow path running through Oeta, thus enabling the Persians to encircle the Greeks and thereby overcome Leonidas, after whose defeat the barbarians gained entrance into Greece.