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 Heraea, after proceeding about fifteen stades from Heraea, you cross the Ladon, and from there you arrive at the Erymanthus after approximately twenty stades. According to the Arcadians’ account, the boundary separating Heraea from Elis is the river Erymanthus, but the Eleans claim that the tomb of Koroibos marks the border of their territory.