Geographically, ancient Arcadia occupied the highlands at the centre of the Peloponnese. To the north, it bordered Achaea along the ridge of high ground running from Mount Erymanthos to Mount Cyllene; most of Mount Aroania lay within Arcadia. To the east, it had borders with Argolis and Corinthia along the ridge of high ground running from Mount Cyllene round to Mount Oligyrtus and then south Mount Parthenius. To the south, the border Laconia and Messenia ran through the foothills of the Parnon and Taygetos mountain ranges, such that Arcadia contained all the headwaters of the Alpheios river, but none of the Eurotas river. To the south-west, the border with Messania ran along the tops of Mount Nomia, and Mount Elaeum, and from there the border with Elis ran along the valleys of the Erymanthos and Diagon rivers. Most of the region of Arcardia was mountainous, apart from the plains around Tegea and Megalopolis, and the valleys of the Alpheios and Ladon rivers.