Passage 3.20.6
ἐπὶ θαλάσσῃ πόλισμα Ἕλος ἦν, οὗ δὴ καὶ Ὅμηρος ἐμνημόνευκεν ἐν καταλόγῳ Λακεδαιμονίων· οἵ τʼ ἄρʼ Ἀμύκλας εἶχον Ἕλος τʼ ἔφαλον πτολίεθρον. Hom. Il. 2.584 τοῦτο ᾤκισε μὲν Ἕλιος νεώτατος τῶν Περσέως παίδων, Δωριεῖς δὲ παρεστήσαντο ὕστερον πολιορκίᾳ, καὶ πρῶτοί τε ἐγένοντο οὗτοι Λακεδαιμονίων δοῦλοι τοῦ κοινοῦ καὶ εἵλωτες ἐκλήθησαν πρῶτοι, καθάπερ γε καὶ ἦσαν· τὸ δὲ οἰκετικὸν τὸ ἐπικτηθὲν ὕστερον, Δωριεῖς Μεσσηνίους ὄντας, ὀνομασθῆναι καὶ τούτους ἐξενίκησεν εἵλωτας, καθότι καὶ Ἕλληνας τὸ σύμπαν γένος ἀπὸ τῆς ἐν Θεσσαλίᾳ ποτὲ καλουμένης Ἑλλάδος.
On the seacoast lay a small city named Helos, which even Homer has mentioned in his catalogue of the Lacedaemonians: "Those who held Amyclae, and Helos by the sea" (Homer, Il. 2.584). Helos was founded by Helios, the youngest son of Perseus. Later, the Dorians captured the city by siege, and these inhabitants became the first slaves of the commonwealth of Lacedaemon, called Helots after their true condition. In time, the term prevailed, such that even subsequent servile classes whom the Dorians acquired (although these later were Messenians by descent) also came to be known as Helots. This resembles how the Greeks collectively gained their name “Hellenes” from the place known as Hellas, located originally in Thessaly.