The Romans did not believe this. They embarked on the Second Punic War confident of victory. Now they had a strong navy, and they designated two uses for it. The first was to take a Roman army under the consul Publius Cornelius Scipio to engage Hannibal in Spain and so neutralize him. The second was to send the other consul, Titus Sempronius Longus, to invade North Africa and conquer Carthage. This might have worked, but the Romans moved too slowly. Seeking a base in the Po Valley, the Carthaginian army under Hannibal marched through southern Gaul and across the Alps into northern Italy. Why did the Carthaginians not invade Italy by sea? Because, now that it had a navy, Rome could blockade any fleet that tried to carry an army along the Spanish coast and down into the Tyrrhenian. Moving elephants around was not easy, either—but the land route, including the perils of crossing the Alps, seemed (for all its difficulties) the only practicable choice. By the fall of 218 B.C.E. Hannibal and his army were among friendly Gauls in the Po. In December, the Romans lost the Po valley entirely to Hannibal.
And so began the Second Punic War (218–202 B.C.E.). When Hannibal began his legendary march with his twenty-one war elephants into northern Italy, he had an army of fewer than 35,000 men with which to confront a total Roman force of 700,000 infantry and 70,000 cavalry (not all of which, of course, could be marshaled together at the same time).
It is still a matter of argument among scholars which route Hannibal might have taken; the most favored view is that he led his army over the Western Alps, via the Mont Cenis pass. Even if he did, the conditions they all encountered were appalling; the descending path was so narrow and steep as to be nearly impassable to horses at one point, let alone to elephants. Landslides had carried away much of the mountain face. But, disheartened as many of his troops were, Hannibal was able to show them something of their destination from the top of the pass; on a clear day, you could see “the actual view of Italy, which lies so close under these mountains that when both are viewed together the Alps stand to the whole of Italy in the relation of a citadel to a city.”
One might have supposed that the odds were so much in Rome’s favor as to render Hannibal’s invasion hopeless. There is still disagreement over the usefulness of those elephants to Hannibal’s campaign, but there is little doubt that they terrified many a Roman soldier, and the effort of getting these great beasts sliding and stumbling over the rocks and through the ice and snow of the Alps must have struck most of those who saw or even heard about it as astonishing. The march from Carthago Nova (Cartagena) had taken five months, and fifteen days had been spent in crossing the Alps. Hannibal arrived in Italy with his force reduced to 12,000 African and 8,000 Iberian foot soldiers, backed up by only 6,000 horseback—and the remaining elephants, of which about half had died on the way. He was, however, able to pick up some reinforcements in northern Italy from the formidable Cisalpine Gauls, who were no doubt attracted by the prospect of loot in Rome.
Rome, of course, had long known that Hannibal was coming. The first encounter between a Roman army, two legions led by Publius Cornelius Scipio, and Hannibal’s forces took place near Ticino, in northern Italy—gateway to the plains through which an army could move south toward Rome—in 218 B.C.E. The engagement was won by Carthage, so convincingly that thousands of tribesmen of the Boii, hitherto allied to Rome, defected to Hannibal’s side. Like a snowball gathering mass as it rolls downhill, Hannibal’s army grew as it moved south. It crushed the Romans at the Battle of Trebia, crossed the Arno swamps, kept going past Faesulae (Fiesole) and Arretium (Arezzo), and reached Lake Trasimene in the spring of 217 B.C.E. Here, it was confronted by an army led by the consul Gaius Flaminius. It was another rout. Apparently, the Romans failed to see the Carthaginians, hidden by early-morning mist on the high ground beside the lake. By the end of that morning, 15,000 Romans were dead, including the luckless Flaminius.
The Roman response to this disaster was to appoint a dictator to lead its army. The tactics followed by this supremo, Quintus Fabius Maximus, earned him the nickname of “Cunctator,” “the Delayer.” Instead of confronting Hannibal’s army head-on, he chose to follow and harass it, in the hope of distracting and enfeebling it without a definitive engagement. But Hannibal’s forces kept marching unstoppably south, down past Rome, toward the Adriatic coast. Before long, the Romans had tired of delays and longed for a decisive, head-on encounter with Hannibal’s army. On August 2, 216 B.C.E., sixteen Roman legions advanced to battle against the Carthaginians near the town of Cannae, in Apulia, south of Rome. The result was the bloodiest and most costly defeat Rome had ever suffered, or ever would.
At Cannae, in one day, Hannibal’s army slaughtered some 50,000 of the Romans and their allies, out of 75,000–80,000 men who took the field. For comparison, one should consider that on the first day of the Battle of the Somme in 1916, there were some 57,000 British casualties, most of whom survived; fewer than 20,000 were killed outright, and the weapons they faced were German machine guns, not Punic spears and swords. The sheer efficiency of the slaughter Hannibal’s army inflicted on the Romans is amazing. Roman losses in a single day at Cannae were almost as great as American combat losses (58,000) in the entire Vietnam War. And it all happened within about nine hours, on a late-spring or early-summer day, blindingly hot, fogged with the clouds of dust kicked up by thousands of men in their relentless, terminal struggle. Varro, the Roman commander, had put the mass of his infantry in the center, leaving his wings, with cavalry, weak and mobile. This was the classical deployment. But Hannibal reversed it, concentrating his weight of infantry on the flanks. In this way, the Romans were soon enveloped, and then cut off from retreat by a Carthaginian cavalry charge across their rear. When the Romans tried to retreat, they were massacred.
They had little experience of defeat, certainly none on this scale. Defeat did not make sense to the Roman army. Rome was first and foremost a military state. The prime qualification for citizenship was the ability to bear arms against her enemies. The Roman army was organized as a militia: service in it was an inflexible condition of citizenship, and by the time of the Punic Wars, it was a highly sophisticated and organized machine.
Its higher officers were aristocrats, but the centurions, who commanded the basic fighting units (“centuries” of one hundred men) were commoners, from the same social class as the line soldiers. This contributed greatly to esprit de corps, as did the frequent swearing of loyalty oaths. The army had never previously lost a major battle against a foreign enemy, and this time the scale was near apocalyptic. In terms of discipline, arms, disposition of forces, and chain of command, the Roman army was meticulously organized against such an event.
The key figure in this organization was the centurion, who had been chosen for his valor and efficiency in leadership. The centurions, as John Keegan has pointed out, were “long-service unit leaders drawn from the best of the enlisted ranks, [who] formed the first body of professional fighting officers known to history.” They were the backbone of the army, the repository of its accumulated service skills, and it was due to them and the example they set that the Romans fought better and with more tenacity than any other tribe or nation in the known world. The centurions turned soldiering into a self-sufficient profession; they did not see their work as a way of entry to the governing class; this was what they were born and trained to do, and there lay much of their strength.