Passage 5.1.1
ὅσοι δὲ Ἑλλήνων Πελοποννήσου πέντε εἶναι μοίρας καὶ οὐ πλείονάς φασιν, ἀνάγκη σφᾶς ὁμολογεῖν ὡς ἐν τῇ Ἀρκάδων οἰκοῦσιν Ἠλεῖοι καὶ Ἀρκάδες, δευτέρα δὲ Ἀχαιῶν, τρεῖς δὲ ἐπὶ ταύταις αἱ Δωριέων. γένη δὲ οἰκεῖ Πελοπόννησον Ἀρκάδες μὲν αὐτόχθονες καὶ Ἀχαιοί· καὶ οἱ μὲν ὑπὸ Δωριέων ἐκ τῆς σφετέρας ἀνέστησαν, οὐ μέντοι Πελοποννήσου γε ἐξεχώρησαν, ἀλλὰ ἐκβαλόντες Ἴωνας νέμονται τὸν Αἰγιαλὸν τὸ ἀρχαῖον, νῦν δὲ ἀπὸ τῶν Ἀχαιῶν τούτων καλούμενον·
As for those Greeks who say that the Peloponnese consists of five divisions and no more, they are compelled to admit that the Eleans and Arcadians occupy one of them—the Arcadian; the second is that of the Achaeans; and upon these follow the three Dorian divisions. Now, the peoples occupying the Peloponnese are the Arcadians and the Achaeans, both originally indigenous. Of these, the Achaeans were displaced from their homeland by the Dorians, yet they did not at least depart from the Peloponnese entirely; instead, expelling the Ionians, they settled what was formerly called Aegialos, but now is named from these Achaeans.