Passage 10.20.8
οὗτοι οὖν διαβαίνουσιν ἐν τῇ νυκτὶ διανηχόμενοι ὧδε τὸ λιμνῶδες τοῦ ποταμοῦ· καὶ τὰ ὅπλα, τοὺς ἐπιχωρίους θυρεούς, ἐποιεῖτο ἕκαστος ἀντὶ σχεδίας, οἱ δὲ αὐτῶν μήκιστοι διελθεῖν ἐμβαδὸν τὸ ὕδωρ ἐδυνήθησαν. οἱ δὲ Ἕλληνες οἱ ἐπὶ τῷ Σπερχειῷ ---πυνθάνονται γὰρ ὅτι κατὰ τὸ ἕλος διέβη μοῖρα τῶν βαρβάρων---αὐτίκα ἐς τὸ στράτευμα ἀναχωροῦσι, Βρέννος δὲ τοῖς περὶ τὸν Μαλιακὸν κόλπον οἰκοῦσι ζευγνύναι τὸν Σπερχειὸν ἐπέτασσεν· οἱ δὲ ἤνυον τὸ ἔργον σπουδῇ, τῷ τε ἐκείνου δέει καὶ ἀπελθεῖν ἐκ τῆς χώρας σφίσιν ἐπιθυμοῦντες τοὺς βαρβάρους μηδὲ ἐπὶ πλέον κακουργεῖν μένοντας.
Thus, they crossed during the night, swimming through the marshy area of the river in the following manner: each man used his shield, a native shield, as a raft; the tallest among them were able to proceed by wading through the water. When the Greeks stationed at the Spercheios learned that a division of the barbarians had passed through the marsh, they immediately retreated to their main force. Meanwhile Brennus ordered the inhabitants around the Malian Gulf to bridge the Spercheios River. They completed the work swiftly, driven both by their fear of him and by their desire for the barbarians to depart from their land, lest they remain and commit further atrocities.