What were the key factors enabling Hannibal to achieve victory against overwhelming odds at Cannae? Hannibal’s battlefield genius was multifaceted. A master of the unexpected, he was unpredictable and capable of non-linear thought—what today we would call “thinking outside the box.” He had the uncanny ability of grasping at a glance the advantages and disadvantages of terrain and weather. He understood perfectly well the strengths and weaknesses of the diverse components of his multi-ethnic army, and how to utilize each to his greatest advantage. Most importantly, he understood his enemies, perhaps better than they understood themselves. His tactical vision is reflected in the manner in which he deployed his forces to face the massive Roman army at Cannae and in his ability to implement his battle plan with clockwork precision. With a virtuosity resembling Capablanca’s brilliance on the chessboard, he achieved what lesser mortals would have regarded as impossible.
On that fateful morning of August 2, 216 BCE, on the plain by Cannae, the Roman army formed facing south/southwest on the right of the Aufidus (now Ofanto) river, with Hannibal’s forces looking north/northeast, neither army at a disadvantage by being blinded by the sun. It is said that a hot wind—the Volturnus—may have blown dust onto the faces of the Romans during the course of the day, but this may have been a circumstance invented by the pro-Roman chroniclers to help explain their defeat. The battlefront was over a mile wide, with 150,000 men prepared to engage in the greatest death struggle of Antiquity.
Let us try to visualize the scenario. It’s mid-morning. Hannibal is on horseback on a slight acclivity, casting his gaze over the plain of Cannae, together with his brother Mago and a small group of officers. The Roman army under consuls Lucius Aemilius Paullus and Caius Terentius Varro is deploying for battle. It is the largest Roman army ever assembled, eight Roman and eight allied legions, 16 legions total, and there are Romans filling the horizon right and left as far as the eye can see. Gisgo, one of the officers, whispers, “Hannibal, there are a lot of Romans there!” The Carthaginian commander replies, “Yes, Gisgo, but you don’t seem to have noticed a very important thing.” “What, my general?” “Among all those Romans, there isn’t a single one named Gisgo!” Gisgo breaks out laughing and is joined by the officer corps, and pretty soon laughter reverberates through the assembled Carthaginian forces. Hannibal could have added, “and among them, there is also no Hannibal!”
The Romans deployed as follows. The equites, numbering 2,400 (or 3,200, if we accept the enhancement of 400 per legion) were on the right wing, commanded by Aemilius Paullus. The allied cavalry, numbering 7,200 (or 9,600), formed the left wing, and was under the command of Terentius Varro. The center, led by Minucius and Servilius, consisted of the massed infantry forces, placed in more compact and deeper formation than was usual for a Roman army. Their number was 80,000 minus the forces left to guard the Roman camps on both sides of the river. The front line consisted of skirmishers.
Hannibal’s army also had cavalry contingents on both flanks. On the Carthaginian left, facing the 2,400-3,200 Roman equites, Hannibal placed his 6,000-strong heavy Celtic and Iberian horse, led by Hasdrubal (no relation to Hannibal’s brother by that name). On the right wing, he deployed the Numidian horse, led by Hanno (or Maharbal), numbering 4,000, and facing the 7,200-9,600 allied horse. In the center he placed his weakest infantry forces, some 30,000 (minus the men left to defend his camp on the left side of the river). They consisted of Gauls interspersed with contingents of more reliable Iberians. He kept his 10,000 elite African veterans (many wearing armor and weapons captured from the Romans at the battle of Lake Trasimene the previous year) as a reserve force, positioning 5,000 on each side. The Carthaginian center formation, directly under the command of Hannibal and his brother Mago, advanced and took position as a convex semicircle (as seen from the Roman side). In front was a line of skirmishers.
Hannibal had to have planned his troop deployment well before the battle, it could not have been an improvisation conceived on the spot while the Roman army was moving into place. Why did Hannibal choose to position his forces as he did? How was he able to predict the movements of his enemies? Did he recognize a fatal flaw in the Roman formation?
It can be argued that what doomed the Romans was their elitism, which rendered them predictable. Hannibal knew that the Roman nobility would ride on the right, the place of honor, and not together with their “lesser” peers, the Italian allies. If the Romans had divided their total cavalry into two equal forces, deployed on either side of the field, the outcome of the battle might have been quite different. But they predictably placed the smaller elite Roman force on the right, creating a fatal vulnerability. Hannibal deployed against them the heavy Celtic and Iberian horse under Hasdrubal, outnumbering them by more than two to one and practically assuring a swift victory on the flank nearest the river. The amazing thing is that he did so without creating a comparable vulnerability on his own right flank, where his cavalry was vastly outnumbered.
Hannibal’s cavalry force consisted of two contingents with completely different capabilities: Celtic/Iberian and Numidian. The heavy Celtic and Iberian riders formed a shock force that would crush their outnumbered Roman counterparts, the cavalry battle becoming compacted between the river and the Roman right infantry flank, to the point that part of the riders had to dismount in order to fight, lacking sufficient room to maneuver. The Numidian horse, on the other hand, which Hannibal placed on his right wing, was a highly mobile force, specializing in hit and run clashes. While for the Italian allies horses were forms of transport taking their riders into battle, the Numidians, who practically grew up on horseback, were one with their mounts, with man and animal functioning as one. They were the best, the most agile and versatile cavalry force in the world in their time. Their tactics involved advancing and retreating, circling and changing directions, closing in to strike and immediately withdrawing too far away to be struck, hit and run, materialize and vanish in a deadly ballet of supreme horsemanship. They were the ideal forces to harass and keep busy the larger contingent of allied horse on the Roman left, immobilizing and pinning down their less mobile adversaries and thus negating the advantage of their numerical superiority.
As the Celtic and Iberian horse routed the Roman cavalry, rather than chase after the few survivors, the disciplined riders under Hasdrubal rode swiftly behind the battlefield to fall upon the back of the allied horse at the opposite side, the forces that were being kept in check by the whirling Numidians. Surprised by the thundering charge, the allied cavalry under Varro panicked and broke, the riders fleeing from the field with tremendous losses, being chased by the Numidians. Varro managed to escape and reached safety in Venusia, 10 miles away, with only 70 riders. The heavy horse under Hasdrubal, eschewing pursuit once more, wheeled around and fell upon the back of the struggling Roman army, again displaying total and perfect discipline in the implementation Hannibal’s master plan. In the meantime, the Carthaginian general had sprung a deadly trap hidden in plain sight—in the very plain the Romans had chosen because there no ambush would be possible!
Following exchanges between the skirmishers, which included Cretan archers on the Roman side and Balearic slingers on the Carthaginian, the massed Roman legions in the center charged, confident of crushing the brave but less disciplined and vastly outnumbered Gauls and Iberians facing them. The Roman battle plan was sound and would have worked under normal circumstances. Their massive army, many men deep, would punch through the enemy center like a gigantic battering ram, cutting Hannibal’s army in half and mopping up the defeated enemy right and left of the broken center. But it was not to be—these were not normal circumstances: they were facing Hannibal, perhaps the greatest military genius in history. The battering ram encountered quicksand.