Passage 7.6.3
τὰ δὲ ἐς πόλεμον τοιάδε ἦν τοῖς Ἀχαιοῖς. κατὰ μὲν τὴν ἐς Ἴλιον ἐπιστρατείαν Ἀγαμέμνονος Λακεδαίμονα ἔτι καὶ Ἄργος οἰκοῦντες μεγίστη τοῦ Ἑλληνικοῦ μοῖρα ἦσαν· κατὰ δὲ τὴν Ξέρξου καὶ Μήδων ἐπὶ τὴν Ἑλλάδα ὁδὸν οὔτε Λεωνίδᾳ τῆς ἐξόδου τῆς ἐς Θερμοπύλας εἰσὶν οἱ Ἀχαιοὶ δῆλοι μετεσχηκότες οὔτε Ἀθηναίοις ὁμοῦ καὶ Θεμιστοκλεῖ πρὸς Εὐβοίᾳ καὶ Σαλαμῖνι ναυμαχήσαντες, οὐδὲ σφᾶς κατάλογος συμμάχων ἔχει Λακωνικὸς ἢ Ἀττικός.
The Achaeans' role in warfare was as follows. At the time of Agamemnon's expedition against Ilium, when they still inhabited Lacedaemon and Argos, they formed the greatest portion of the Greek forces. However, during the invasion by Xerxes and the Medes into Greece, the Achaeans are nowhere recorded to have participated either in Leonidas' expedition to Thermopylae or in the sea battles alongside the Athenians and Themistocles near Euboea and Salamis; nor do they appear in the lists of allies made by the Lacedaemonians or the Athenians.