An army of Gauls under Brennusinvade Greece. A section of the army, commanded by Bolgios, crushes a Macedonian army led by Ptolemy Keraunos, who is killed in the battle. At the narrow pass of Thermopylae, on the east coast of central Greece, Brennus' forces suffer heavy losses while trying to break through the Greek defence comprising the Phocians and the Aetolians. Eventually Brennus finds a way around the pass but the Greeks escape by sea. Brennus pushes on to Delphi where he is defeated and forced to retreat, after which he dies of wounds sustained in the battle. His army falls back to the river Spercheios where it is routed by Thessalians and Malians. Some of the survivors settle in a part of Asia Minor that will eventually be called Galatia, while some settle in Thrace, founding a short-lived city-state named Tylis.
With the death of Ptolemy Keraunos, the previous King of Macedonia, Antipater II becomes king again. However, his new reign lasts only few months before he is killed by his cousin Sosthenes who becomes the new King of Macedonia.
The Phocians are readmitted into the Amphictyonic League after they have joined in the defence of Delphi against the Gauls.
The Carthaginians and the Romans agree to support each other against a common foe. The Carthaginians give Rome money and ships in their fight against Pyrrhus, the king of Epirus.
Pyrrhus realizes that he cannot capture Rome and suggests peace terms to the Romans. Pyrrhus sends his chief advisor, Cineas, to Rome to negotiate a peace. Cineas demands that the Romans halt their aggression against the Greeks of southern Italy and restore the lands the Romans have taken from the Bruttii, the Apulians, and the Samnites. The Romans reject his demands, largely at the instigation of the former Roman censor, Appius Claudius Caecus.
In renewed fighting, Pyrrhus of Epirus, leading the combined Tarantine, Oscan, Samnite, and Greek forces, wins a 'Pyrrhic victory' against the Romans led by consul Publius Decius Mus at the Battle of Asculum, called such because his victory comes at a great cost to his own forces. Pyrrhus is reported to have said afterwards, "One more victory against the Romans and we shall be utterly ruined!" Disheartened, Pyrrhus retires to Tarentum and sends Cineas to make renewed peace overtures to Rome. These talks are inconclusive.