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The Mystery of Cannae: Re-examining Hannibal's Greatest Victory

Poppies blooming in a field close to Barletta, Italy. Haiku by the author. The Battle of Cannae, on August 2, 216 BCE, pitted genius against overwhelming odds, brains vs. brawn, a master tactician facing overconfident commanders. It was Hannibal’s masterpiece, perhaps the most astonishing military victory in history, still assiduously studied in military academies worldwide, and the inspiration for a number of relatively recent war engagements, from the Schlieffen Plan in WWI to General Schwarzkopf’s envelopment of Saddam Hussain’s army in the first Gulf War. It has generated an extensive body of literature, ranging from specialized books and studies published in many languages to chapters and discussions in numerous textbooks. And yet, despite the level of interest generated, many aspects of the clash between the multi-ethnic Carthaginian forces and the largest army Rome had ever raised remain obscure and controversial. This may be in part the result of the loss or destruction of the Carthaginian records of the event, coupled with the distortions and contradictions in the pro-Roman accounts, amounting to what, in today’s terms, we would call a campaign of disinformation.

The first point of controversy concerns the actual strength of the armies that took part in the celebrated battle. After being defeated in the cavalry encounter at the Ticinus river (218 BCE), at the battle of the river Trebia (218 BCE), and at Lake Trasimene (217 BCE), the Romans decided to raise a massive army to get rid of Hannibal once and for all. Polybius (3:107) tells us that the Romans recruited no less than eight legions, to be matched by an equal number of legions from their Italian allies, for a grand total of 16 legions, and that the numerical strength of each legion was increased from 4,000 to 5,000. Consequently, the size of the infantry forces marshaled by the Romans totaled 80,000. Hannibal’s army at Cannae, on the other hand, numbered 40,000 foot soldiers, giving the Romans a 2:1 numerical advantage. These numbers are usually accepted as valid by most historians and there is no reason to challenge them. The only additional factor is the number of troops staying back in the Roman and Carthaginian camps and therefore not actually participating in the battle. The 10,000 number usually given seems too large, as this was a decisive conflict and both sides would have wanted to field the largest possible number of actual combatants in the field. It must also be remembered that the camps would have included a large number of support personnel that typically accompanied ancient armies in the field, and these may have led to the inflated number reported by the sources.

The question, though, is the size of the cavalry forces that fought in the battle of Cannae, and especially the total strength of the Roman horse. According to the classical sources (Polybius and Livy), the Roman defeats at the Ticinus, Trebia, and Trasimene battles were in part the direct result of numerical superiority of the Carthaginian horse. It stands to reason, then, that in recruiting cavalry complements for their enlarged legions, the Romans would also have increased the size of the equestrian forces accompanying each legion, probably from 200 to at least 300, or perhaps even 350 or 400. Polybius (3:107) actually states that “on occasions of exceptional gravity” the Romans increased the size to 300, and that the numbers of the allied cavalry were required to be “three times as numerous as the Roman.” Hannibal’s successive defeats of three Roman armies certainly constituted an “occasion of exceptional gravity,” for the very survival of the Republic was at stake. It makes sense to assume that the cavalry, whose weakness had contributed to the previous defeats, was particularly strengthened. Polybius indicates elsewhere (4:25) that a typical legion of his day included 300 horse riders (rather than 200) as standard number, which makes an enhanced figure of 400 for “special occasions” even more likely. If we use the figure of 400 per Roman legion (or a total of 3,200 for the eight legions at Cannae), and triple that number for the allied legions, giving each a strength of 1,200 (or 9,600 total for the eight allied legions), we arrive at a combined cavalry number of 12,800 riders. This would mean that the Romans not only outnumbered Hannibal’s infantry forces, but also held numerical superiority in cavalry (Hannibal’s numbering 10,000), contrary to the usual narrative. Even if we accept only an increment for “occasions of exceptional gravity” of 300 rather than 400, this would total 2,400 (300 x 8) Roman and 7,200 (900 x 8) allied cavalry, or a total of 9,600. It can be concluded, therefore, that the Romans had at least practical parity, if not superiority, to Hannibal’s horsemen.

Polybius (3:107), though, lists the strength of the Roman horse only as being “over 6,000.” Why this discrepancy? Perhaps one reason can be found in the fact that the Romans consistently rationalized their defeats by attributing them to Hannibal’s superior cavalry numbers, so that accepting that they actually held superiority, or at least parity, in cavalry, at the moment of their greatest disaster, would have made their defeat that much more shameful. Polybius wrote 50 years after the battle, and although he may have interviewed some survivors, he did not witness the event. The Romans prided themselves of being the best warriors of their time, a self-image challenged by Hannibal’s victories. While necessarily recognizing and even reluctantly admiring Hannibal’s genius (for how could they have been defeated by a lesser general?), they needed a way to excuse and rationalize their own failure. Hannibal’s alleged cavalry superiority of 10,000 against the “over 6,000” Roman riders provided such an explanation.

Incidentally, Gregory Daly has argued (in his book on Cannae) that the larger numbers for the Roman horse are unlikely because “early encounters between Roman and Numidian cavalry suggest no significant qualitative difference between the two” and that therefore “the annihilation of the citizen cavalry at Cannae can be largely explained by their being greatly outnumbered.” As we will see in a following article, though, there was a different reason for the defeat of the Roman and allied horse, which did not preclude their actual numerical superiority. It can also not be argued that the Romans would not have been able to raise a larger cavalry force due to a shortage of horses or riders, for even after Cannae they continued recruiting large cavalry contingents for scores of legions; clearly, no such shortage existed. We must therefore conclude that at Cannae Hannibal’s army of 40,000 foot soldiers and 10,000 riders faced the vastly numerically superior Roman force of 80,000 infantry and 12,800 (or at least 9,600) cavalry.

A second point of controversy concerns the question of who was actually in command of the massive Roman army that fought at Cannae? Following the disastrous defeat of the Roman army and the death of its commanding officer, Consul Gaius Flaminius, at Lake Trasimene in 217 BCE, Fabius Maximus was appointed dictator for six months. Realizing that he was no match for Hannibal on the battlefield, he wisely followed the crafty Carthaginian with his army at a distance, harassing the enemy but refusing to face him in battle (an approach that has become known as “Fabian tactics”). This earned him the derogatory nickname of “cunctator”, or “delayer.” Roman pride and bellicosity simply could not tolerate the situation for long, and at the end of his term the Senate replaced him with two new consuls who were given the specific assignment of dealing with Hannibal once and for all. The traditional account names the consuls as the prudent and aristocratic Lucius Aemilius Paullus and the brash and impulsive Gaius Terentius Varro, a plebeian, the son of a butcher. Varro was a demagogue and a braggart, and it was supposedly he who was in command at the time of the battle, and thus deserves the blame for the worst military disaster in the history of Rome.

But was Varro really in command? And did Aemilius Paullus advise against engaging Hannibal in battle, as the classical accounts (Polybius and Livy) claim? The consuls alternated command on a daily basis, and we are told that Aemilius Paullus refused to commit himself to battle the previous day, but on August 2, when Varro was in charge, the hot-headed plebeian consul ordered the Roman army to deploy for battle. In the first place, this does not make sense, because the stated mission of the largest Roman army ever assembled was to face and defeat Hannibal in battle—clearly both consuls were interested in engaging and destroying the Carthaginian invader. But perhaps Aemilius Paullus’s alleged reluctance resulted from the battlefield being favorable to the tactics of Hannibal, a factor overlooked by the supposedly impulsive Varro?