from the book, "Petrified Lightning"
During the third century b.c. the Romans issued picturesque copper bars to commemorate pigs. The Romans were not inclined to commemorate casually; when they did, it was for very good reason. In this case they considered the honored pigs to be thoroughly deserving.
The army of Caesar was under heavy attack by the army of Pyrrhus (319—272 b.c.), whose use of war elephants was a very effective offense. The Romans, completely unprepared for this type of warfare, were being pushed into an imminent defeat, and the footsoldiers fought with real desperation.
The din of battle was overwhelming to a large group of pigs being kept in the Roman encampment as a ready supply of food. The noise so unsettled them that they panicked and tore down the fences that enclosed them. As the pigs ran helter—skelter between the feet of the advancing war elephants, the huge beasts also panicked. Uncontrollable, they reared up, throwing off the riding soldiers along with the mahots (drivers) and fled the battlefield in complete disarray. With them went Pyrrhus's army.
The Romans achieved complete victory but in a manner so unexpected that the army of Caesar just stood and watched dumbfounded as the enemy fled in total confusion. For years afterward, to eat a pig or, for that matter, to harm one was forbidden. In recognition of the "service" of the pigs, the Roman government issued commemorative copper bars to honor the unofficial pig soldiers.