A victory gained at too great a cost.
King Pyrrhus of Epirus gained such a victory over the Romans in 279 BC at the battle of Asculum in Apulia. The battle was fought between Pyrrhus' army and the Romans, commanded by Consul Publius Decius Mus. The Epiriotic forces, although they won the battle, suffered severe losses of the elite of their army.
The phrase 'pyrrhic victory' is an allusion to the battle. John Dryden's translation of Plutarch's Pyrrhus, 75 AD reports that:
"... they had fought till sunset, both armies were unwillingly separated by the night, Pyrrhus being wounded by a javelin in the arm, and his baggage plundered by the Samnites, that in all there died of Pyrrhus's men and the Romans above fifteen thousand. The armies separated; and, it is said, Pyrrhus replied to one that gave him joy of his victory that one other such would utterly undo him. For he had lost a great part of the forces he brought with him, and almost all his particular friends and principal commanders; there were no others there to make recruits, and he found the confederates in Italy backward."