Sicyon or Sikyōn was an ancient Greek city state situated in the northern Peloponnesus between Corinth and Achaea on the territory of the present-day regional unit of Corinthia. The ruins lie just west of the modern village of Sikyona. An ancient monarchy at the times of the Trojan War, the city was ruled by a number of tyrants during the Archaic and Classical period and became a democracy in the 3rd century BC. Sicyon was celebrated for its contributions to ancient Greek art, producing many famous painters and sculptors. In Hellenistic times it was also the home of Aratus of Sicyon, the leader of the Achaean League.

Achaea or Achaia is the northernmost region of the Peloponnese, occupying the coastal strip north of Arcadia. Its approximate boundaries are: to the south, Mount Erymanthus; to the south-east, Mount Cyllene; to the east, Sicyon; and to the west, the Larissos river. Apart from the plain around Dyme in the west, Achaea is generally a mountainous region.