Fortuitously the right bank of the Alpheios Valley became a defensive zone for the protection of central Arcadia. During the so-called Dorian invasion starting about 1000 BC iron-age highlanders (Dorians) from central Greece overran the bronze-age coastal regions of the Peloponnesus, expelling or subjugating the Mycenaean population there, but could not ascend the right-bank mountains to take central Arcadia. The population there maintained its culture (Arcado-Cypriot) and political independence. The Dorians kept the valley, which accounts for the predominance of Doric architecture at Olympia.
