Passage 1.41.2
ἐντεῦθεν ὁ τῶν ἐπιχωρίων ἡμῖν ἐξηγητὴς ἡγεῖτο ἐς χωρίον Ῥοῦν ὡς ἔφασκεν ὀνομαζόμενον, ταύτῃ γὰρ ὕδωρ ποτὲ ἐκ τῶν ὀρῶν τῶν ὑπὲρ τὴν πόλιν ῥυῆναι· Θεαγένης δέ, ὃς τότε ἐτυράννει, τὸ ὕδωρ ἑτέρωσε τρέψας βωμὸν ἐνταῦθα Ἀχελῴῳ ἐποίησε. καὶ Ὕλλου πλησίον τοῦ Ἡρακλέους μνῆμά ἐστιν ἀνδρὶ Ἀρκάδι Ἐχέμῳ τῷ Ἀερόπου μονομαχήσαντος· καὶ ὅστις μὲν Ἔχεμος ὢν ἀπέκτεινεν Ὕλλον, ἑτέρωθι τοῦ λόγου δηλώσω, τέθαπται δὲ καὶ Ὕλλος ἐν τοῖς Μεγάροις. αὕτη καλοῖτο ἂν ὀρθῶς στρατεία τῶν Ἡρακλειδῶν ἐς Πελοπόννησον ἐπὶ Ὀρέστου βασιλεύοντος.
From there, our local guide conducted us to a place which he claimed is called Rous ("Stream"), because once a flow of water descended this way from the mountains above the city. Theagenes, who at that time was tyrant, diverted the water in another direction and established there an altar to Acheloos. Near to it is the tomb of Hyllos, the son of Herakles, who fought in single combat against Echemos, an Arcadian, son of Aeropos. Who this Echemos was that killed Hyllos I shall explain elsewhere, but Hyllos too is buried at Megara. This expedition of the Heracleidae against the Peloponnese in the reign of Orestes might rightly be called their first campaign.