The Battle of Cannae, 216 BC, remains one of the greatest military reversals of all time. The Roman army, which outnumbered its Carthaginian enemies and was undoubtedly better equipped, should have logically won an easy victory. However, Hannibal and his army arrived at Cannae coming off two consecutive victories over Roman legions, at Trebia and Trasumennas (Polybius briefly mentions, but never names, a third Carthaginian victory); Hannibal had, indeed, proven to be the greatest weapon Carthage could field.
Hannibal marched his army to the nearby town of Cannae, and set up his camp along the river Aufidus. When he learned of the Roman approach, he sent his cavalry and skirmishing troops to attack the legions while they were still marching in column. The attack was indecisive, and the Romans likewise camped along the Aufidus. Disagreement between Varro and Paulus prevailed over the next several days. On the day of Paulus’s command, the Roman army did not form up for battle; the veteran consul knew better than to engage the Carthaginians in an open plain, where the superior Carthaginian cavalry would reign supreme. Furthermore, according to Livy, Hannibal established his camp in such a position that the wind blew a constant butt of dust in the Romans’ direction. Despite these disadvantages, the following day and, according to Polybius and Livy, against the urges of Paulus, Varro formed the Roman legions up for battle in what would become the greatest massacre of a pitched battle in recorded history.
According to Polybius, Rome abandoned its tradition of granting two consuls two legions each in the special case of the Second Carthaginian war. Eight legions were amassed by Rome to confront Hannibal; the consuls Lucius Aemilius Paulus and Gaius Terentius Varro were assisted in the command of this huge fighting force by the previous year’s consuls, Marcus Atilius and Gnaeus Servilius. As is predictable in times of great crises, the Roman legions provided were increased in strength from 4000 to 5000 legionnaires each. About 1500 Roman cavalry and 4500 allied cavalry supported these legions; lighter infantry was also present.
Hannibal, champion of Carthage, brought to the fight an army of 40,000 infantry containing elements of Spanish, Celtic, and African troops, and 10,000 supporting cavalry, likewise consisting of Spanish, Gallic, and Numidian regiments. Slingers and other skirmishing infantry supported the Carthaginian army.
The Roman army crossed the river Aufidus; placing the river on his right, Varro supported his right flank with Roman cavalry, led by Paulus, and his left with allied cavalry. Skirmishing troops and light infantry were arrayed in front of the heavy legionary infantry; Polybius confirms this as a standard Roman battle setup.
Hannibal’s formations were much more remarkable. Covering the Carthaginian left flank were Spanish and Gallic cavalry, headed by Hannibal’s brother Hasdrubal, across from the Roman cavalry. Hannibal arranged his Numidian cavalry on his right flank, opposite Varro and the cavalry of Rome’s allies. Spanish infantry, equipped with large shields and swords designed for Romanesque close order battle, and Celtic warriors, armed with longswords, formed the center of Hannibal’s line. On either side of these European regiments were hardened African contingents, armed with the arms and armor of defeated Roman legionnaires, the core of Hannibal’s infantry. What made the formation of Hannibal’s army unique was its crescent shape, which would prove vital to the battle’s outcome.
The battle begins with standard skirmishing by light troops on either side as the infantry advanced; meanwhile, the cavalry corps of each side charged forward, colliding violently in the middle. On the Roman right, Paulus and his Roman cavalry crashed into their Spanish and Gallic opponents. Polybius describes the following engagement: “…The struggle that ensued was truly barbaric; for there were none of the normal wheeling evolutions, but having once met they dismounted and fought man to man.” This strange departure from typical cavalry warfare is attributed by Livy to the Aufidus on one side of the fight and the massed heavy infantry on the other. Neither cavalry force would want to circle too far and wind up drowning in the river, nor would they wish a simultaneous engagement with both enemy cavalry and heavy infantry. The Carthaginian cavalry eventually overcame their Roman foes, and chased them from the field. Paulus was not cut down in the pursuit, as he entered the fight of the infantry in the middle of the field, where he believed the battle would be decided. He could not have been more wrong.
The infantry engaged as the Roman cavalry was driven from the field; though better equipped and trained, the Roman line could not break the Spaniards and Celts, who they engaged first, as made possible by the crescent shape of Hannibal’s line. However, besides its unique shape, or perhaps because of it, the line was also thinly stretched; as the Roman legions pressed inward to the present engagement, their massed numbers and sheer weight broke through the thin line of Spanish and Celtic infantry. The Romans pursued their prey as the Spaniards and Celts fled between the African contingents. Hannibal’s African infantry then collapsed in on the flanks of the Romans, who were now surrounded by fresh and equally well-equipped troops.
On the Roman left flank, Varro and the allied cavalry engaged the Numidians in an indecisive cavalry battle. Polybius and Livy offer conflicting descriptions of this engagement. Polybius claims that the Numidians had a strange style of fighting but were holding their own against Varro, until Hasdrubal arrived fresh from his victory over the Roman cavalry; as Hasdrubal charged into Varro’s cavalry, the Roman allies fled. Hasdrubal sent his Numidians after Varro, then turned and launched coordinated cavalry charges into the rear of the Roman infantry with his Spanish and Gallic horses. Livy details a complicated Carthaginian tactic wherein a small force of Numidians pretended to flee the field, hid in the cavalry engagement, picked up Roman equipment from the battlefield, then joined the rear ranks of the Roman infantry when no one would notice. This hidden corps of assassins then cut into the unsuspecting Roman rear.
Whether by skill or guile, the Carthaginian cavalry proved superior to its Roman counterpart. Varro no longer commanded the Roman infantry, who were now pressed by fresh troops from all sides. Paulus went down fighting in this hopeless slaughter, along with Servilius and Atilius, all three of whom Polybius honors as having served their Republic with great courage and valor.
At day’s end, after the Roman infantry had been killed to the last man, Polybius tallies the Roman dead at just over 40,000 infantry and 5000 cavalry. The Carthaginians suffered 4000 dead Celts, 1500 dead Spanish and African infantry, and 200 dead cavalry.
The Battle of Cannae proved two flaws in the Roman war machine, one major and one potential.
The Roman legions lacked sufficient cavalry to reliably defeat a Carthaginian army in the field; Hannibal’s cavalry supremacy at Cannae allowed him to launch attacks into the unprotected Roman rear and cut off the only avenue of escape, leading to the slaughter in a single day of the greatest Roman army assembled up to that point.
Cannae also highlighted the potential of conflicting command in Roman armies. The daily transfer of absolute power from one consul to the other led to disaster as Varro had the Senate-given authority to march his army into a disadvantageous battle against Hannibal contrary to all the advice and counsel provided by the more experienced Paulus.
These two flaws resulted in Rome’s inability to muster an army to fight Hannibal on the Italian peninsula; not until the successful campaign of Scipio in Africa would Rome escape near catastrophe in the Second Punic War.