Battle of Heraclea
The Battle of Heraclea in 280 B.C. was fought between the forces of Rome and the forces of Pyrrhus in southern Italy. The Romans under Publius Valerius Laevinus had about 35,000 men, Pyrrhus about 30,000. After a terrible struggle Pyrrhus routed the Roman cavalry by judicious use of his elephants which the Romans had never before encountered. He then drove the Roman infantry back across the Siris in great disorder. Victory that day belonged to Pyrrhus. The Romans had anywhere from 7,000 to 15,000 dead while Pyrrhus had lost anywhere from 4,000 to 11,000. Looking at the terrible losses that he suffered, Pyrrhus is said to have commented, "One more such victory and I am lost."
Encyclopedia of Military History, Dupuy & Dupuy, 1979