Passage 4.15.4
τότε δὲ οἱ Μεσσήνιοι Λακεδαιμονίοις συμβάλλουσιν ἐν Δέραις καλουμέναις τῆς σφετέρας, ἔτει πρώτῳ μετὰ τὴν ἀπόστασιν· ἀπῆσαν δὲ ἀμφοτέροις οἱ σύμμαχοι. καὶ νίκη μὲν ἐγένετο οὐδετέρων σαφής, Ἀριστομένην δὲ ἔργα φασὶν ἀποδείξασθαι πλέον τι ἢ ἄνδρα ἕνα εἰκὸς ἦν, ὥστε καὶ βασιλέα μετὰ τὴν μάχην ᾑροῦντο αὐτόν, ἦν γὰρ καὶ γένους τῶν Αἰπυτιδῶν·
Then the Messenians fought the Lacedaemonians at a place in their own territory called Derae, in the first year after their revolt. Both sides were without their allies. The victory was clearly gained by neither army, but Aristomenes was said to have performed deeds surpassing those of one man so greatly that after the battle they elected him king, as indeed he belonged to the family of the Aepytidae.