Peloponnesus, the main peninsula of southern Greece. It is linked to central Greece by the Isthmus of Corinth. The area of this mountainous region is about 8,000 square miles (20,720 km2). The subdivisions of the Peloponnesus in classical times were Achaea, Arcadia, Argolis, Corinth, Elis, Laconia, Messenia, and Sicyonia, and the chief city-states were Sparta, Corinth, and Argos. During the Middle Ages the peninsula was called Morea.