Passage 10.20.1
πάρεστι δέ, ὅστις ἐθέλοι καὶ ἀνταριθμῆσαι τούς τε ἐπὶ βασιλέα Ξέρξην ἐς Πύλας καὶ τοὺς τότε ἐναντία Γαλατῶν ἀθροισθέντας. ἐπὶ μέν γε τὸν Μῆδον ἀφίκοντο τοσοίδε Ἑλλήνων· Λακεδαιμόνιοι οἱ μετὰ Λεωνίδου τριακοσίων οὐ πλείονες, Τεγεᾶται πεντακόσιοι καὶ ἐκ Μαντινείας ἴσοι, παρὰ δὲ Ὀρχομενίων Ἀρκάδων εἴκοσί τε καὶ ἑκατόν, ἀπὸ δὲ τῶν ἄλλων χίλιοι τῶν ἐν Ἀρκαδίᾳ πόλεων, ὀγδοήκοντα δὲ ἐκ Μυκηνῶν καὶ ἐκ Φλιοῦντος διακόσιοι, διπλάσιοι δὲ τούτων Κορίνθιοι· παρεγένοντο δὲ καὶ Βοιωτῶν ἑπτακόσιοι ἐκ δὲ Θεσπείας καὶ ἐκ Θηβῶν τετρακόσιοι. χίλιοι δὲ Φωκέων ἐφύλασσον μὲν τὴν ἀτραπὸν ἐν τῇ Οἴτῃ, προσέστω δὲ τῷ παντὶ Ἑλληνικῷ καὶ ὁ ἀριθμὸς ὁ τούτων.
Anyone who wishes may compare the numbers of those assembled against King Xerxes at Thermopylae with those later gathered to oppose the Gauls. The Greeks came against the Persian in these numbers: no more than three hundred Spartans under Leonidas; five hundred men from Tegea, and an equal number from Mantineia; from Orchomenus in Arcadia one hundred and twenty; and from the other cities of Arcadia a thousand. From Mycenae there were eighty; from Phlius two hundred; the Corinthians supplied twice that number. Seven hundred Boeotians were present, and from Thespiae and Thebes four hundred. A thousand Phocians guarded the path through Mt. Oeta, and their number too must be added to the entire Greek force.