Passage 10.23.5
ἅμα δὲ τῷ ἡλίῳ ἀνίσχοντι οἱ Ἕλληνες ἐπῄεσάν σφισιν ἐκ τῶν Δελφῶν, οἱ μὲν ἄλλοι τὴν ἐπὶ τὸ στράτευμα εὐθεῖαν, οἱ Φωκεῖς δὲ ἅτε καὶ μᾶλλον ἔχοντες τῶν χωρίων ἐμπείρως κατέβησάν τε διὰ τῆς χιόνος κατὰ τὰ ἀπότομα τοῦ Παρνασσοῦ καὶ ἔλαθον κατὰ νώτου γενόμενοι τοῖς Κελτοῖς, ἠκόντιζόν τε ἐς αὐτοὺς καὶ ἐτόξευον σὺν οὐδενὶ ἀπὸ τῶν βαρβάρων δείματι.
As soon as the sun rose, the Greeks advanced against them from Delphi; the rest went straight against the enemy army, but the Phocians, being more familiar with the terrain, descended through the snow down the steep slopes of Parnassus, and unnoticed, came around to the rear of the Celts, casting javelins and arrows upon them, showing not the slightest fear of the Barbarians.