The Greek overseas expansion of the 8th cent. BC founded a number of towns that became the centers of a new, thriving Greek territory. They were on both coasts from the Bay of Naples and the Gulf of Taranto southward. Unlike Greek Sicily, Magna Graecia began to decline by 500 BC, probably because of malaria and endless warfare among the colonies. Only Tarentum (now Taranto) and Cumae remained individually very significant.

Magna Graecia was the center of two philosophical groups in the 6th cent. BC, that of Parmenides at Elea and that of Pythagoras at Crotona. Through Cumae especially, the Etruscans of Capua and the Romans came into early contact with Greek civilization. The following are the chief cities of Magna Graecia (those colonized from Greece, except Thurii and Elea, go back to the 8th or early 7th cent. BC; those colonized locally are perhaps a century younger)—on the east coast from north to south, Tarentum (colonized from Sparta), Metapontum (from Achaea), Heraclea (from Tarentum), Siris (from Colophon), Sybaris (from Achaea), Thurii (from Athens, replacing Sybaris), Crotona (from Achaea), Caulonia (from Crotona), Epizephyrian Locris (from Locris); on the west coast from north to south, Cumae (from Chalcis), Neapolis (now Naples; from Cumae), Paestum, or Posidonia (from Sybaris), Elea (from Phocaea in Ionia), Laos (from Sybaris), Hipponium (from Epizephyrian Locris), and Rhegium (now Reggio de Calabria; from Chalcis).