Herculea was a southern Italian colony of the classical Greek city Megara

Megara

Megara is an ancient city in Attica, Greece. It lies in the northern section of the Isthmus of Corinth opposite the island of Salamis, which belonged to Megara in archaic times, before being taken by Athens. Megara was one of the four districts of Attica, embodied in the four mythic sons of King...

 (or The Megarid) which was located on the isthmus

Isthmus

An isthmus is a narrow strip of land connecting two larger land areas usually with waterforms on either side.Canals are often built through isthmuses where they may be particularly advantageous to create a shortcut for marine transportation...

 across to the Peloponnese, adjacent to Corinth

Corinth

Corinth is a city and former municipality in Corinthia, Peloponnese, Greece. Since the 2011 local government reform it is part of the municipality Corinth, of which it is the seat and a municipal unit...

 and Attica

Attica

Attica is a historical region of Greece, containing Athens, the current capital of Greece. The historical region is centered on the Attic peninsula, which projects into the Aegean Sea...

. Herculea, though not referred to often in the writings of historians at the time such as Herodotus and Thucydides, was a considerable step towards discovery for the more often than not isolationist Peloponnesian League

Peloponnesian League

The Peloponnesian League was an alliance in the Peloponnesus from the 6th to the 4th centuries BC.- Early history:By the end of the 6th century, Sparta had become the most powerful state in the Peloponnese, and was the political and military hegemon over Argos, the next most powerful state...

related city/states.