Strabo Geography 8.2.3

[3] The Corinthian Gulf begins, on the one side, at the outlets of the Evenus (though some say at the outlets of the Acheloüs, the river that separates the Acarnanians and the Aetolians), and, on the other, at Araxus; ¹ for here the shores on either side first draw notably nearer to one another; then in their advance they all but ² meet at Rhium and Antirrhium, where they leave between them a strait only about five stadia in width. Rhium, belonging to the Achaeans, is a low-lying cape; it bends inwards (and it is in fact called “Sickle “). ³ It lies between Patrae and Aegium, and possesses a temple of Poseidon. Antirrhium is situated on the common boundary of Aetolia and Locris; and people call it Molycrian Rhium. ⁴ Then, from here, the shoreline on either side again draws moderately apart, and then, advancing into the Crisaean Gulf, it comes to an end there, being shut in by the westerly limits of Boeotia and Megaris. ⁵ The perimeter of the Corinthian Gulf if one measures from the Evenus to Araxus, is two thousand two hundred and thirty stadia; but if one measures from the Acheloüs, it is about a hundred stadia more. Now from the Acheloüs to the Evenus the coast is occupied by Acarnanians; ⁶ and thence to Antirrhium, by Aetolians; but the remaining coast, as far as the Isthmus, belongs to ⁷ the Phocians, the Boeotians and Megaris—a distance of one thousand one hundred and eighteen stadia. The sea from Antirrhium as far as the Isthmus ⁸ is called Alcyonian, it being a part of the Crisaean Gulf. Again, from the Isthmus to Araxus the distance is one thousand and thirty stadia. Such, then, in general terms, is the position and extent of the Peloponnesus, and of the land that lies opposite to it across the arm of the sea as far as the recess; and such, too, is the character of the gulf that lies between the two bodies of land. Now I shall describe each part in detail, beginning with the Eleian country.