The Pyrrhic War (/ˈpɪrɪk/ PIRR-ik; 281–275 BC) was a conflict fought by Pyrrhus of Epirus and his allies against the Roman Republic, supported by its allies, and Carthage. Fought mainly in Magna Graecia and Sicily, Pyrrhus first intervened at the invitation of the Italiote Greeks against Roman expansion. However, his aims in the war became oriented towards establishing hegemony over southern Italy and Sicily. Initially meeting some success, his aims were left unfulfilled after his campaign in Sicily stalemated against Carthaginian resistance and Rome forced his withdrawal from Italy in 275 BC. The first major conflict involving Rome and one of the Hellenistic powers, Rome's victory showed its emergence as a major Mediterranean power.
Prior to the war, the Romans had expanded for some decades into southern Italy, defeating most notably the Samnites. They also started to conclude alliances with the Greek city-states of Magna Graecia. The outbreak of a new conflict between one of those allies, Thurii, and a Samnite-led alliance led to Roman intervention. The Tarentines, seeking to prevent continued Roman intervention in southern Italy, attacked a Roman fleet sailing in their waters contrary to a previous treaty and marched on Thurii, deposing the pro-Roman government there. After rejection of a Roman ultimatum in early 281 BC, war was declared. Cognisant of their weakness in the field, the Tarentines sought foreign support in the form of Pyrrhus of Epirus, who landed at Tarentum with reinforcements in the winter of 281/80 BC.