Pyrrhic victory

A Pyrrhic victory is a victory that comes at such a high cost that it's questionable if it was worth it. It comes from the Battle of Heraclea and the Battle of Asculum that the Romans fought with King Pyrrhus in southern Italy. Pyrrhus "won" both battles, but his losses were so horrific that he is quoted as saying "One more such victory, and I am lost!"

Sources

Encyclopedia of Military History, Dupuy & Dupuy, 1979