The wiser heads in Tarentum saw no reason to object, but the popular party was furious and began again to look eastwards for someone to fight their battles for them. The arrival at this moment of a small Roman squadron in forbidden waters was probably excusable as a war measure in defence of Greek allies, but it was a formal breach of the treaty of 302 BC with Tarentum.
The populace of Tarentum lost its head, insulted the Roman mission of apology, made trouble among other Greek cities, and prepared to avenge their grievance by war.
Once again sudden help came to Tarentum from beyond the Adriatic Sea. Pyrrhus, king of Epirus, was nephew and successor of Alexander 'the Molossian' who had brought help before. He had also married a daughter of Agathocles of Syracuse, and seems to have regarded himself as a predestined successor, a part for which he was in many way well suited. Sicily rather than Italy, which was to serve as a stepping stone, was probably his real objective from the beginning. He had the reputation of a fire-brand among the 'Successor States' (to Alexander the Great's empire), whose kings seem to have sent him considerable forces, on the understanding that he did not employ them near home.
What Alexander the Great had done to the Persian empire, Pyrrhus evidently thought was possible also in the west, and Tarentum seemed the necessary base for such conquests.
This was not quite what the populace of Tarentum had intended, and the declaration of martial law by the advance guard which garrisoned their city in 280 BC cooled their love for Pyrrhus very quickly. The other Greek cities had not asked for him, and the Romans had no intention of resigning their protectorate to the newcomer.
Pyrrhus evidently had not heard much about the Romans. What he heard now evoked his respect. Still more, what he saw, in hard fighting at Heraclea and at Ausculum.
(It is to Pyrrhus we owe the expression of 'a Pyrrhic victory'. For after having defeated the Romans at Heraclea in 280 BC by inspired use of his elephant corps, but otherwise very considerable cost to his own forces, he reported to have said that one more such victory would lose him the war.)
The Italian dominion was not for him. He had come too late. And if Carthage was the real enemy, as he learned from Agathocles of Syracuse, there was nothing to be gained by quarreling with Rome, too.
Carthage naturally though otherwise and sent a squadron up to the Tiber mouth to offer help against Pyrrhus. The terms of the third treaty with Carthage now concluded in effect an alliance between Rome and Carthage against Pyrrhus.
The effect was to limit Pyrrhus' career in the west to aggression against the Greek states which he had nominally come to protect, for it destroyed his hopes of allying with either Rome or Carthage against the other.
Veterans of Agathocles, settled now at Messana, offered their help, but Campania and most of the south gave Pyrrhus no encouragement. Only Etruria thought the tide had turned agaisnt Rome, only to quickly discover its mistake.
After two campaigns in which, though he always won battles, Pyrrhus was losing more men than he could afford he moved on to Sicily (278 BC) and the Romans had little difficulty in dealing with his friends and rear guards on the Italian mainland.
The Carthaginians had not waited to be attacked. When Pyrrhus sailed for Sicily, they were besieging Syracuse, his necessary base, and looking for him with their fleet. He evaded their ships however and drove off their field army, captured the cities of Panormus and Eryx and refused their offer to surrender everything in Sicily except for Lilybaeum, which they direly needed if they sought to keep their hold on Sardinia.
But all the while his losses had been heavy and his reinforcements few. Tarentum was hard pressed by the Romans and between them and the Carthaginian fleet he might have been trapped in Sicily.
So in a desperate attempt he returned once more into Italy, to fight one more campaign. He was severely defeated, as the Romans had meanwhile learned how to deal with his spearmen and elephants.
The tide having turned against him in force Pyrrhus returned home.
His parting words were memorable,
'What a battlefield I am leaving for Carthage and Rome !'
The tale goes that Pyrrhus later died during an assault on Argos, where an old woman seeing him fighting her son sword to sword in the street below supposedly threw a roof tile on his head. Although other sources read that he was assassinated by a servant.