The Pyrrhic War (280–275 BC) was largely fought between the Roman Republic and Pyrrhus, the king of Epirus, who had been asked by the people of the Greek city of Tarentum in southern Italy to help them in their war against the Romans.
A skilled commander, with a strong army supported by war elephants (which the Romans were not experienced in facing), Pyrrhus enjoyed initial success against the Roman legions, but suffered heavy losses even in these victories. Plutarch wrote that Pyrrhus said after the second battle of the war, "If we are victorious in one more battle with the Romans, we shall be utterly ruined." He could not call up more men from home and his allies in Italy were becoming indifferent. The Romans, by contrast, had a very large pool of military manpower and could replace their losses. This is the source of the expression "Pyrrhic victory", a victory that inflicts losses the winner cannot afford in the long term.
Worn down by the battles against Rome, Pyrrhus moved his army to Sicily to war against the Carthaginians instead. After several years of campaigning there (278–275 BC), he returned to Italy in 275 BC, where the last battle of the war was fought, ending in Roman victory. Following this, Pyrrhus returned to Epirus, ending the war. Three years later, in 272 BC, the Romans captured Tarentum.
The Pyrrhic War was the first time that Rome confronted the professional mercenary armies of the Hellenistic states of the eastern Mediterranean. Rome's victory drew the attention of these states to the emerging power of Rome. Ptolemy II, the king of Egypt, established diplomatic relations with Rome. After the war, Rome asserted its hegemony over southern Italy.
By 290 BC, at the end of the three Samnite Wars, Rome had established her hegemony over parts of central and southern Italy, cemented through alliances with various Italic peoples in central Italy. To the south of the Roman sphere of influence there were a few city-states founded by Greek settlers from the 8th to the 6th century BC (primarily on the coasts of Calabria and Basilicata and in eastern and southern Sicily).