Passage 8.26.3
ἐς δὲ τὴν Ἠλείαν κατιὼν ἐξ Ἡραίας στάδια μέν που πέντε καὶ δέκα ἀποσχὼν Ἡραίας διαβήσῃ τὸν Λάδωνα, ἀπὸ τούτου δὲ ἐς Ἐρύμανθον ὅσον εἴκοσιν ἀφίξῃ σταδίοις. τῇ δὲ Ἡραίᾳ ὅροι πρὸς τὴν Ἠλείαν λόγῳ μὲν τῷ Ἀρκάδων ἐστὶν ὁ Ἐρύμανθος, Ἠλεῖοι δὲ τὸν Κοροίβου τάφον φασὶ τὴν χώραν σφίσιν ὁρίζειν.
Going down into Elis from Heraia, after proceeding about fifteen stades from Heraia, you cross the Ladon, and from there you arrive at the Erymanthos after approximately twenty stades. According to the Arcadians’ account, the boundary separating Heraia from Elis is the river Erymanthos, but the Eleans claim that the tomb of Koroibos marks the border of their territory.