The Greek colonies in southern Italy began to be planted at nearly the same time as in Sicily. They eventually lined the whole southern coast, as far as Cumae on the one sea and Tarentum on the other. They even surpassed those in Sicily in number and importance; and so numerous and flourishing did they become, that the south of Italy received the name of Magna Graecia. Of these, two of the earliest and most prosperous were Sybaris and Croton, both situated upon the gulf of Tarentum, and both of Achaean origin. Sybaris was planted in 720 BC and Croton in 710 BC. For two centuries they seem to have lived in harmony, and we know scarcely anything of their history till their fatal contest in 510 BC, which ended in the ruin of Sybaris. During the whole of this period they were two of the most flourishing cities in the Hellenic World. Sybaris in particular attained to an extraordinary degree of wealth, and its inhabitants were so notorious for their luxury, effeminacy, and debauchery, that their name has become proverbial for a voluptuary in ancient and modern times. Croton was the chief seat of the Pythagorean philosophy. Pythagroras was a native of Samos, but emigrated to Croton, where he met with the most wonderful success in the propagation of his views. He established a kind of religious brotherhood, closely united by a sacred vow. They believed in the transmigration of souls, and their whole training was designed to make them temperate and self-denying. The doctrines of Pythagoras spread through many of the other cities of Magna Graecia.

Of the numerous other Greek settlements in the south of Italy, those of Locri, Rhegium, and Tarentum were the most important. Locri was founded by the Locrians from the mother-country in B.C. 683. The laws of this city were drawn up by one of its citizens, named Zaleucus, and so averse were the Locrians to any change in them, that whoever proposed a new law had to appear in the public assembly with a rope round his neck, which was immediately tightened if he failed to convince his fellow-citizens of the necessity of the alteration. Rhegium, situated on the straits of Messina, opposite Sicily, was colonized by the Chalcidians, but received a large body of Messenians, who settled here at the close of the Messenian war. Anaxilas, the tyrant of Rhegium ca. 500 BC, was of Messenian descent. He seized the Sicilian Zancle on the opposite coast, and changed its name into Messana, which it still bears. Tarentum was a colony from Sparta and was founded about 708 BC. After the destruction of Sybaris it was the most powerful and flourishing city in Magna Graecia, and continued to enjoy great prosperity till its subjugation by the Romans. Although of Spartan origin, it did not maintain Spartan habits, and its citizens were noted at a later time for their love of luxury and pleasure.