Setting: a war already going badly for Rome
The Battle of Cannae was fought on 2 August 216 BCE, according to the traditional Roman calendar date, near the town of Cannae in Apulia in southern Italy. It belongs to the Second Punic War, which Hannibal Barca of Carthage had carried into Italy after crossing the Alps in 218 BCE. Before Cannae, he had already beaten Roman armies at the Trebia and at Lake Trasimene. Rome’s answer had been the cautious strategy of Quintus Fabius Maximus, who avoided open battle and shadowed Hannibal. By 216 BCE the Senate and the people wanted a decisive result.
The armies
Our main sources, Polybius and Livy, were writing well after the event, and Polybius is usually treated as the more careful. Their figures are the best available, but they are not exact.
According to Polybius, the Romans fielded about 80,000 infantry and 6,000 cavalry, including allies, against about 40,000 infantry and 10,000 cavalry on Hannibal’s side. Even if the numbers are somewhat off, the Roman advantage in infantry was large, and the Carthaginian advantage lay in cavalry.
Hannibal’s army was a mixed force. It included Libyan infantry, Spanish and Gallic troops, and Numidian horsemen, partly held together by Hannibal’s own authority. Carthaginian armies relied heavily on this kind of hired and allied troops, a subject covered in the article on Carthaginian mercenaries. The Roman army combined Roman citizen soldiers, serving in the Roman legions, with Italian allies.
Command and the plan
Both consuls, Lucius Aemilius Paullus and Gaius Terentius Varro, were present. Ancient sources say they alternated the supreme command day by day, and that Varro was in command on the day of the battle. Later Roman writers blamed him heavily, which may be unfair, since the tradition was shaped by hindsight and by political rivalry.
Hannibal chose ground on the open plain beside the river Aufidus, which suited his cavalry. According to Polybius, he placed his Gallic and Spanish infantry in a forward-curving centre, with the Libyans on either side and the cavalry on the wings. The Romans, in contrast, packed their infantry unusually deep to drive through the centre.
The double envelopment
The fighting followed a pattern that has been studied ever since:
- On Hannibal’s left, his Spanish and Gallic horse defeated the Roman cavalry opposite them and then rode behind the Roman line to attack the other Roman cavalry.
- In the centre, Hannibal’s front units gave ground slowly in good order, so that the curve flattened and then bent inward. The Romans pressed forward into what had become a pocket.
- The Libyan infantry on each side turned inward and struck the Roman flanks.
- Once the Carthaginian cavalry returned to close the rear, the Roman army was surrounded and compressed, unable to use its numbers.
This is the Hannibal double envelopment: the attacker engages the front, then closes around both flanks and the rear. The result was less a battle than a massacre of troops who could not manoeuvre. Because the Romans were crowded together, their numerical advantage worked against them.
The cost to Rome
The losses were severe. Polybius gives about 70,000 Roman and allied dead, while other ancient sources give lower figures. Even the lower estimates make Cannae one of the worst defeats in Roman history. Many senior officers and a large number of senators were among the dead, and Paullus is said to have been killed in the fighting. Varro survived and escaped.
The strategic effects were also serious. A number of southern Italian communities, including the important city of Capua, went over to Hannibal in the following months, though many Roman allies stayed loyal. Rome raised new forces, including recruits it would not normally have used, and it avoided a repeat of the open-battle confrontation. Survivors of Cannae were sent to serve in Sicily as a form of punishment.
Why Hannibal did not win the war
Hannibal did not march on Rome after Cannae. Ancient writers debated this, and modern historians generally doubt he had the siege equipment or supply needed, as well as the political aim of destroying Rome. He hoped to break up Rome’s alliance network in Italy, and that largely failed. Rome kept its core allies, avoided battle in Italy, and carried the war to Spain and later to North Africa. Hannibal was eventually recalled to defend Carthage and was defeated at Zama in 202 BCE by Scipio. The full course of that conflict is described in the overview of the Punic Wars.
Legacy
Cannae became a model of tactical encirclement in later military study. It is also a reminder that numbers and courage do not decide a battle alone: ground, cavalry, discipline and command all matter. For Rome, the defeat is often seen as part of how the Republic learned to endure setbacks, though that reading is, in part, a Roman story told afterwards. The Roman Senate that guided the war through these years kept its nerve, and that political resilience helped shape the later pattern of Roman expansion.