The site of Paestum was occupied during prehistory. Near the basilica were found objects dating from the Paleolithic to the Bronze Age; near Porta Giustizia, remains of huts have been discovered; At the temple of Athena and towards Porta Aurea, a Neolithic settlement was highlighted.
One imagines that two villages could have existed on the small hills corresponding to the basilica and the temple of Athena, and that between them a river would have crossed the expanse which was subsequently occupied by the forum.

The Eneolithic (Italian Chalcolithic) left more traces with the necropolis of Gaudo, about 1.5 km to the north.

From Sybaris to Poseidonia

The most important Greek colonies of the Mediterranean were founded in Asia Minor and in Magna Graecia (Magna Grecia, corresponding to southern Italy and Sicily), of which Poseidonia (Paestum) was a part.

But, we lack accurate information about the circumstances of the founding of the city, which took place around the middle of the seventh century BC.
However everything seems to come from the city of Sybaris, which established commercial colonies along the Tyrrhenian coast, like Laos, then further north at the mouth of the Sele where was founded a sanctuary dedicated to Hera, close to the future place of Paestum.
Strabo, the famous historian and geographer who lived at the time of Augustus (between 60 and 20 BC), reports indeed that around – 600, the sybarites installed a fortified place near the mouth of the Sélé River.

Sybaris, on the Gulf of Taranto, which is the motherland of Poseidonia, was founded in 720 BC by some Achaeans.
This city was notoriously prosperous, known for its luxury and power, as reported by Diodorus Siculus in the 1st century BC, writing that “the sybarites were slaves of their bellies and lovers of luxury.”

This expansion of the colonies was thus linked to the need of the Sybarites to open a trade route between the Ionian Sea and the Tyrrhenian Sea, cutting through the Apennine Mountains, thus avoiding the bypass of the Calabrian coast and the Strait of Messina by sea.
Called Poseidonia in honor of the god of the sea Poseidon, it was strategically located at the crossroads of trade routes between the Ionian Basin, the Tyrrhenian Sea, and the Italic regions of the interior.
Thus, the Sybarite trade developed as well by sea, between the Greeks, Etruscan and Latin, as on the ground, in contact with the native populations.

It was clearly in the second half of the 7th century that Poseidonia was developed. In a necropolis located just outside the enclosure, was found Corinthian Greek material which show that the city existed in 625 BC.