Ancient Rome is often thought of as consistently victorious but its defeat at the hands of Carthage in 216 B.C. remains one of the most studied and imitated battles of all time.
Military Historian Robert L. O'Connell tells the story of Carthage's unexpected victory in The Ghosts of Cannae: Hannibal and the Darkest Hour of the Roman Republic.
O'Connell tells NPR's Neal Conan that while the Carthaginian commander, Hannibal, was a brilliant tactician, he really shouldn't have gone into this battle expecting to win.
"Carthage was essentially a naval power and Hannibal was a land general," he says. "He was invading a country that was basically strange territory, and it had huge manpower resources, which Carthage didn't have."
Still, the Battle of Cannae marked a stunning victory for Carthage over Rome. Hannibal and his army enveloped a larger Roman army, annihilating it and killing more Romans in one day than the United States lost in all of the Vietnam War.
"The ghosts of Cannae" refers to the Roman soldiers who survived the slaughter — and had to carry their loss home with them.
"After they lost the battle, the Romans were so mortified that they actually banished these guys to Sicily as garrison troops," O'Connell says.
The ghosts were in Sicily for 13 years, until Roman general Publius Cornelius Scipio, known as Scipio Africanus, recruited them for his campaign in Africa.
"He went to Sicily to stage the invasion," O'Connell says, "and built out of the survivors of Cannae a new army that eventually beat Hannibal."
The historian says that Hannibal's defeat came about because — after 13 years of believing Rome's allies would dessert the oppressor and rally to his cause — he failed to recognize the personal relationships Rome had established between its leading citizens and the leading citizens of its allies.
"Hannibal looked at Rome's alliance structure through an X-ray, and all he saw were the bones," O'Connell says. "What he really needed was an MRI that would have shown the connective tissue."
Hannibal never fully understood the strength of Rome, which is why — despite winning battle after battle — he was ultimately unable to break it.