Following Hannibal’s master plan to the letter, Hasdrubal, in charge of the victorious heavy horse, instead of pursuing the few fleeing survivors among the Equites, raced with his riders behind the battlefield to fall upon the Allied horse, which, attacked from two directions, broke and fled in a panic, pursued with deadly efficacy by the Numidians. Instead of joining in the chase, Hasdrubal’s heavy horse turned around and descended upon the rear of the Roman infantry as planned, sealing their fate. In retrospect, it is clear that what doomed the Romans at Cannae was above all, their hubris, which made them predictable and resulted in the fatal uneven deployment of their cavalry, a factor Hannibal exploited in his brilliant and deadly battle plan.
A further fascinating aspect of the battle is that the center of Hannibal’s infantry was advanced in the form of a semi-circle. He put his weakest and least reliable men in the center: Gauls, whose discipline was questionable and who had a tendency to run if the going got too tough, interspersed with units of Spanish infantry, known for their bravery. He arranged them in a semi-circle, convex from the point of view of the Romans. The reason for that unusual formation was to ensure that when the Roman army advanced they would make initial contact only with the center of the Carthaginian battle line. The men on both sides of the center, also anxious to clash with the hated enemy, naturally would start converging towards the center. So instead of the Roman army maintaining their initial deployment, they became gradually more and more compacted towards the center in order to be able to fight, just as Hannibal had envisioned.
Following Hannibal’s orders, the Carthaginian center composed of his Gauls and Iberians started a slow measured retreat, their front line flattening out and then, bit by bit, becoming concave, like a huge sack, into which the Romans pursued, thinking they were winning. We are winning! We are pushing the damned Gauls and Spaniards back, they are afraid of us, any moment now they will break and run! Let’s kill them all! The Romans kept advancing, not realizing that they were moving into a trap of Hannibal’s devising. And then, the 10,000 Libyan elite infantry kept on reserve, 5,000 on each side, moved into place and started compressing the Romans from the right and the left, creating chaos and confusion in the trapped Roman juggernaut.
The previous year, at the Battle of Lake Trasimene, Hannibal had been able to capture 15,000 Romans, and despoiled them of their armor, their shields, their swords, their equipment, which was now worn by the elite African troops, who at first sight looked like Romans. So, the men attacking from the sides caused terrible confusion. If you were a Roman soldier, moving with the flow, concentrating on the fight in front of you, you could suddenly be cut down by what appeared to be other Romans at your side, who didn’t look at all like the enemy. For this reason, the Libyans pressing in from the sides were able to get really close without resistance, and as the Roman army became more and more more compacted, they gradually were completely immobilized. The Gauls and Iberians, led by Hannibal himself and his brother Mago, stopped their retreat and are started counterattacking with renewed energy.
The Carthaginian heavy horse stormed and trampled the Romans from the back, and as the Africans pressed like a vise grip from the flanks, the huge mass of Roman soldiers were completely trapped and pressed together until they hardly had space to wield their weapons. Although they were 80,000 strong, the only ones that could actually fight at this point, and barely so, due to lack of space, were the men at the edges, all around the doomed army—those inside could only wait their turn to die. Even though Hannibal had only half their number, he had more that could actually fight, swing their swords and thrust their spears, and also move to allow fresh replacements to take their place. For the Romans it must have been terrifying. Can you imagine being one of the men in the middle? Just waiting your turn to be cut down?
Sadly, this outcome was not the result of Hannibal’s desire to slaughter an entire Roman army, but the consequence of the Romans’ assembling such an enormous force to annihilate him and his men. I am convinced that Hannibal was forced to use the double envelopment as the only possible solution to the problem posed by the numerical superiority of the Roman army. I mean, how can you fight an army of 92,000 with an army of 50,000, unless you immobilize it? And once you have immobilized that army, what can you do? The people inside are not surrendering. They’re all armed. If you don’t continue cutting them down they will fight again.
They will redeploy. So the Romans, by creating their super army, forced Hannibal to find a way to neutralize and annihilate it. See, the battles of those days were not battles of annihilation. They were battles where two armies met, and when one side got the upper hand, the other fled and accepted defeat, with some sort of peace deal following. Usually the defeated army would lose maybe a few hundred or a thousand or two, but nothing like the casualties at Cannae, where 70,000 Romans and some 5,000 of Hannibal’s men perished. The numerical superiority of the Roman army made it impossible to defeat in any other way. Hannibal, contrary to Livy’s propaganda, was not particularly cruel or bloodthirsty. He was a civilized man, a cultured man, an educated man, not some sort of barbarian butcher. I am convinced that he did not rejoice in the death of so many men. He was, in all likelihood, horrified, and contemplated the outcome of his brilliant battle tactics with a heavy heart, but he also knew that there had been no other way. By putting together their enormous army, the Romans forced Hannibal to opt for a tactic with devastating effects. Ironically, in trying to annihilate Hannibal the Romans assured their own annihilation.
It is interesting to note the difference between Polybius and Livy as to how many Romans lost their lives in this battle. Polybius, who is generally regarded as the more trustworthy source, says 70,000. Livy, on the other hand, says about 50,000. That’s a big difference. Well, the problem is that Livy is adding the numbers from what became the official pro-Roman account. He is counting only 6,000 for the Roman horse. But if we add instead the 12,000 we have established as the real size of the cavalry, as clearly Polybius must have, forgetting for a moment that he had previously disguised the number as “over 6,000,” we have enough men on the field to accept 70,000 killed.
The reason why the 70,000 figure is sometimes rejected by modern historians is because it doesn’t seem to add up due to the doctored up cavalry numbers. The higher number of Romans killed according to Polybius can be seen as additional proof that their cavalry was larger than reported. If we accept Polybius’ numbers as correct, we have about 70,000 Romans and over 5,000 on the Carthaginian side, which is an enormous number. The fighting at Cannae took maybe four to six hours, and utilized primarily swords and spears, and yet the casualties were comparable to those of the atom bombing of Nagasaki! Although such numbers in ancient battles are often exaggerated, Delbrück says in his History of Warfare that in the case of Cannae the Polybian numbers are credible, by virtue of the nature of the double envelopment that prevented escape from the trapped army. These casualty numbers are unparalleled in the history of Mediterranean warfare and were not matched until the killing fields of World War I, and then only with the use of machine guns, tanks, bombs, and poison gas.