Helike was an ancient Greek polis (city-state) that was submerged by a tsunami in the winter of 373 BC.

The Achaean League was a Hellenistic-era confederation of Greek city-states on the northern and central Peloponnese. The league was named after the region of Achaea in the northwestern Peloponnese, which formed its original core. The first league was formed in the fifth century BC. The second Achaean League was established in 280 BC. As a rival of Antigonid Macedon and an ally of the Roman Republic, the league played a major role in the expansion of Rome into Greece. This process eventually led to the League's conquest and dissolution by the Romans in 146 BC.