The Roman legion is known to history as one of the elite fighting forces of all time. Its compact legions of 4000-5000 men dominated the ancient world for 800 years.
However, these forces were not invincible, and in the Second Punic War, they met their match in Hannibal Barca. In what was perhaps the single most bloody day in human conflict, he annihilated a much larger force in the battle of Cannae.
Over the intervening millennia, Hannibal’s tactics have become an idealized model, often attempted but rarely attained.
In the third century BC, two empires jousted for dominance in the Mediterranean. The Carthaginian Empire was an old empire descended from the Phoenicians, with its capital in modern Tunisia.
Its power lay in the sea, and it depended on controlling the islands and coastlines of the sea to protect its trading routes.
The upstart Roman Empire depended on its elite army to overawe and subjugate its adversaries.
As the Romans expanded from Italy into the Iberian peninsula, they clashed with the Carthaginians coming the other way.
These clashes set off over a century of warfare between the two states. These were collectively known as the Punic Wars and stretched from 264 BCE to 146 BCE.
The first Punic War (264-241) mainly involved naval warfare, whose main arena of conflict was the island of Sicily. Despite Carthage’s long history of naval dominance, the Romans learned how to compete and ultimately defeated the Carthaginian fleet off the island’s west coast, ending the war in a Roman victory.
Twenty years later, in 219 BC, Hannibal launched a war of revenge against the Roman foe. He struck north from New Carthage (now Cartagena, Spain) toward the Roman city of Saguntum, which he captured in 219. This thrust triggered a Roman declaration of war the following year.
Hannibal portrayed himself as a liberator to peoples subjugated by Rome, including Gauls and Celts living in what is now France, Spain, and northern Italy. He gathered troops from disaffected populations as he advanced through northern Spain, southern Gaul (France), and northern Italy.
Allies were essential to Hannibal’s strategy because Carthage’s weakness was manpower. The core army relied on mercenaries from Africa. Rome, on the other hand, drew from a much larger population base from the city-states of Italy and its own heartland.
Hannibal’s army grew as it crossed the Alps, but, more importantly, he gained a reputation as an almost supernatural general in pitched battles. He was an astute observer of the tendencies of his opponents and repeatedly defeated them in battle over the next several years as he advanced down the Italian peninsula from the north.
After decisive defeats at the battles of Trebia (218) and Trasimene (217), the Romans appointed Fabius Maximus as “dictator” (the Roman term for a temporary war leader) to face Hannibal.
Fabius, recognizing Hannibal’s weakness was his extended supply lines back through Spain to Carthage, embarked on a “Fabian Strategy” of avoiding battle while denying Hannibal supplies as he marched throughout Italy.
Hannibal was too weak for a direct attack on Rome, which was heavily fortified and defended. For a period in 217 and 216, therefore, neither side could really come to grips with the other. However, Fabian’s strategy weakened his position over time.
Hannibal bypassed the main Roman forces and defenses on the western side of the Italian peninsula and instead marched down the Adriatic coast to sway more of the Italian city-states to his side and perhaps establish a supply connection through the boot of Italy back to Carthage.
At the end of his six-month term as a dictator, the Romans grew impatient with Fabius’s attritional strategy and demanded a more aggressive stance toward the invaders.
He was replaced by a duo of proconsuls, the patrician Aemilius Paulus and the commoner Terentius Varro, who were given the largest army Rome had ever raised, 16 legions totaling 80,000 men, with the instructions to confront Hannibal’s much smaller army directly.
The Battle of Cannae
The Roman legions met Hannibal’s 40,000 men and 10,000 cavalry at the small town of Cannae near the Adriatic coast. By this point, Hannibal had gained an almost mythic status as a commander among the Romans.
However, Varro and Paulus felt that their overwhelming numerical superiority almost guaranteed them victory.
Heavy infantry were the strongest Roman forces. Roman legions formed dense blocks of men trained to fight as a unit and move across the battlefield like giant tortoises, nearly invincible as long as they stayed together.
The Romans feared the Carthaginian cavalry, which was the elite of Hannibal’s army. Cavalry were the shock troops of the Carthaginian army, depending on speed and momentum to break up the Roman legions.
On the other side, the Romans used their weaker cavalry mainly as flank protection and for the exploitation of a fleeing enemy. Varro and Paulus concentrated their strength in the center of their line and expected to meet Hannibal’s strength there.
There is some controversy over who was in command of the Roman formation on that day. We do know that Varro and Paulus agreed to a centralized command structure, with each of them commanding on alternate days.
This was the largest army that Rome had ever fielded, so a centralized command structure was a questionable decision. With almost 80,000 men, the Roman line was as much as 2 kilometers long at Cannae.
The ability of any commander to communicate with all his troops using flags and runners during a pitched battle was questionable, at best.
The other part of the command structure was also clouded by history. Polybius, writing decades after the actual events, was friends with Paulus’s grandson, and all other histories of the event are derived wholly or in part from his account of the battle.
Paulus would die during the battle, and Varro left no account of the events of that day. There is evidence that Polybius, not wanting to blame the patrician Paulus for the defeat, scapegoated Varro by writing that he was in charge of the legions on that day.
Hannibal, on the other hand, was in full control of events on the field of battle. He understood the weaknesses of his enemy in mobility and how this would dictate a strategy of making a frontal attack using masses of heavy Roman infantry.
He also understood the aggressive personalities of both Varro and Paulus. Their decision-making was also influenced by the Fabian strategy’s unpopularity and the Roman Senate’s demands to destroy Hannibal’s army.
These things worked together to telegraph the likely Roman plans, such as they were, to Hannibal. He knew they were likely to concentrate their forces to facilitate communication, concentrate their strength, and maximize the impact of their shock infantry. Hannibal, therefore, had little to fear from being enveloped by his numerically superior foes.
The solution, as he saw it, was not to meet strength with strength but to meet strength with bait. The center of his line could bend but not break. Hannibal put his least reliable troops, Celtic and Gallic allies he had recruited, in the center to meet the Roman onslaught.
This deployment was intended to attract the Roman attacks as they also understood the African troops were the best ones in Hannibal’s army. To compensate for the lower quality of the allied troops, Hannibal assumed personal command of this part of the line.
The Carthaginian leader then placed his strongest forces, the African infantry, and cavalry, along the flanks. He delegated command of these forces to his brothers Mago and Hasdrubal with instructions that when his center was pushed toward the banks of the Aufidius River to his rear that they should wheel about the sides and rear of the Roman formation.
The Romans did exactly as expected and, hoping for a breakthrough to the Carthaginian camp on the far side of the river, launched over 70,000 men against the far weaker center of the line. But, despite extreme pressure, the Celts and Gauls, under Hannibal’s direct command, gave ground slowly.
Eventually, the line, which Hannibal originally deployed into a convex arc facing the Romans, bent into a concave shape with its apex on the river bank. It was at this point that both flanks of African troops and cavalry broke around the back of the Roman formation, putting over 70,000 of them in a sack surrounded by Hannibal’s army.
As the encirclement constricted, the Roman forces found it impossible to deploy their superior numbers in the confined space Hannibal’s forces created. The battle degenerated into a massacre. In one of the bloodiest days in human warfare, the Carthaginian forces slaughtered over 70,000 legionnaires. Only about 6,000, including Varro, escaped the carnage.
Hannibal’s losses were less than 6,000 men. But, more importantly, he was left with a functioning army. The Romans were not.
While Cannae was an immense tactical victory for the Carthaginians, Hannibal struggled to turn it into a strategic one. As a result, he bought himself time and won over critical allies that allowed him to keep his army in the field in Italy for years to come. However, his ability to attack Rome itself was no better than it had been before the battle.
Roman losses were a staggering 2.5% of their total population in this one engagement alone. However, given time, they could replace their losses out of their much larger population base. Meanwhile, the Fabian strategy was restored because of a lack of any real alternative.
Significant Roman forces continued to operate along Hannibal’s long supply line, stretching back through Gaul and the Iberian Peninsula. Rome’s navy interdicted any supplies coming across the sea. Although Hannibal’s army had free rein over much of the Roman countryside for years, it slowly withered.
It wasn’t until 210 BCE that Rome finally mounted a counteroffensive under the command of the Scipio Africanus, who had somehow survived Cannae as a young soldier.
Scipio rightly saw Hannibal’s weakness as Spain, not his army in Italy. He seized the Iberian capital of New Carthage, crossed into Africa from there, and defeated Hannibal in the Battle of Zama outside Carthage itself in 201 BCE. Hannibal died in exile 18 years later.
In the centuries since it was fought, Cannae has been held up as the “ideal” battle. Hannibal’s double envelopment is seen as the gold standard of maneuver warfare. However, it has rarely been achieved since then.
Everything has to go right for it to be successful. The attackers have to cooperate and press inward on the center. That center has to bend but not break. Giving ground under pressure without being routed is one of the toughest military maneuvers.
Subsidiary commanders on the wings have to execute their maneuvers at the right time. Wait too long, and the center will collapse. Don’t wait long enough, and you will be attacking into the teeth of the enemy rather than their exposed sides and rear. Having enough force to complete the encirclement is also a challenge.
Changes in technology have both increased the scope and scale of double envelopments. However, they have also increased the complexity of operations necessary to achieve them.
During Operation Barbarossa in 1941, the Germans achieved several double envelopments employing rapid armor strikes supported by aircraft at a scale impossible even a few years earlier. German forces captured half a million Soviet soldiers in one operation around Kyiv alone.
In 1991, the US isolated Iraqi forces in Kuwait using a similar tactic of fixing them in place and then using mobility advantages to move around to their rear and trap thousands of troops in Kuwait.
When the Russians invaded Ukraine in 2022, a key early success by the Ukrainians was preventing an envelopment of Kyiv, causing a collapse of that part of the offensive.
However, the brilliance of Hannibal’s leadership could not overcome the strategic disadvantages that Carthage suffered from against Rome. Carthage depended on quick wars to exercise its technological advantages.
In this way, Carthage resembles Japan in World War II more than any other power. The United States could suffer defeats early in that conflict, but Japan was doomed from the beginning because of the vast disparity of resources between the two powers.
Coming up against Rome, with its resources in manpower to compensate for any advantages it may have had in fighting battles, Carthage found itself stalemated.
While it required the emergence of a great general like Scipio Africanus to defeat Carthage, Rome had the time to let that happen. Carthage did not. Therefore, the ultimate end of the power struggle was always foreordained to be a Roman victory. It takes more than a brilliant victory like Cannae to win a war.
- Alexander, Bevin, How Great Generals Win (New York: W.W. Norton, 1993)
- Cowley, Robert and Geoffrey Parker eds., The Reader’s Companion to Military History (New York: Houghton Mifflin, 1996)
- Keegan, John, A History of Warfare (New York: Vintage, 1993)