Passage 8.5.10
Πολυμήστορι δὲ οὐ γενομένων παίδων παρέλαβεν Αἶχμις τὴν ἀρχήν, Βριάκα μὲν παῖς, Πολυμήστορος δὲ ἀδελφιδοῦς· Αἰγινήτου γὰρ ἦν καὶ Βριάκας, νεώτερος δὲ ἦν Πολυμήστορος. Αἴχμιδος δὲ βασιλεύσαντος Λακεδαιμονίοις ἐγένετο ὁ πρὸς Μεσσηνίους πόλεμος· τοῖς δὲ Ἀρκάσιν ὑπῆρχε μὲν ἐς τοὺς Μεσσηνίους εὔνοια ἐξ ἀρχῆς, τότε δὲ καὶ ἐκ τοῦ φανεροῦ πρὸς Λακεδαιμονίους ἐμαχέσαντο μετὰ Ἀριστοδήμου βασιλεύοντος ἐν Μεσσήνῃ.
Since Polymestor had no sons, Aechmis inherited the kingship. He was the son of Briacas and cousin to Polymestor; for Briacas, too, was the son of Aeginetes, though younger than Polymestor. It was under Aechmis's rule over the Lacedaemonians that the war with the Messenians occurred. From the start the Arcadians felt goodwill toward the Messenians, but at that time they openly joined battle against the Lacedaemonians, siding with Aristodemus, who was then king in Messene.