Passage 7.24.5
ἰόντι δὲ ἐς τὸ πρόσω Σελινοῦς τε ποταμὸς καὶ ἀπωτέρω τεσσαράκοντα Αἰγίου σταδίοις ἐπὶ θαλάσσῃ χωρίον ἐστὶν Ἑλίκη. ἐνταῦθα ᾤκητο Ἑλίκη πόλις καὶ Ἴωσιν ἱερὸν ἁγιώτατον Ποσειδῶνος ἦν Ἑλικωνίου. διαμεμένηκε δέ σφισι, καὶ ὡς ὑπὸ Ἀχαιῶν ἐκπεσόντες ἐς Ἀθήνας καὶ ὕστερον ἐξ Ἀθηνῶν ἐς τὰ παραθαλάσσια ἀφίκοντο τῆς Ἀσίας, σέβεσθαι Ποσειδῶνα Ἑλικώνιον· καὶ Μιλησίοις τε ἰόντι ἐπὶ τὴν πηγὴν τὴν Βιβλίδα Ποσειδῶνος πρὸ τῆς πόλεώς ἐστιν Ἑλικωνίου βωμὸς καὶ ὡσαύτως ἐν Τέῳ περίβολός τε καὶ βωμός ἐστι τῷ Ἑλικωνίῳ θέας ἄξιος.
As one proceeds forward, one reaches the river Selinous, and forty stadia further from Aigion along the seashore is the place Helike. Here was situated the city Helike, and the most sacred sanctuary of Poseidon Helikonios revered by the Ionians. They maintained this worship even when, having been expelled by the Achaeans into Athens, they afterward moved from Athens to the coastal region of Asia; and Poseidon Helikonios continued to be honored among them. Thus, among the Milesians as one goes toward the spring called Biblis, there is an altar of Poseidon Helikonios in front of the city; likewise at Teos there is a precinct and an altar dedicated to Helikonios, which is worthy of viewing.