The Carthaginians and their allies, led by Hannibal, surrounded and practically annihilated a larger Roman and Italian army under the consuls Lucius Aemilius Paullus and Gaius Terentius Varro.

They massed their heavy infantry in a deeper formation than usual, while Hannibal used the double envelopment tactic and surrounded his enemy, trapping the majority of the Roman army, who were then slaughtered.

These tactics proved unpopular with the Romans who, as they recovered from the shock of Hannibal's victories, began to question the wisdom of the Fabian strategy, which had given the Carthaginian army a chance to regroup.

[22] As Polybius noted, the capture of Cannae "caused great commotion in the Roman army; for it was not only the loss of the place and the stores in it that distressed them, but the fact that it commanded the surrounding district".

[28] On the morning of the battle, as the forces drew up, a Carthaginian officer named Gisgo reportedly remarked to Hannibal that the size of the Roman army was astonishing.

Those men, Celtiberians according to Appian and Numidians according to Livy, handed their weapons to the Romans as a sign of good will while retaining hidden short swords in their clothes.

Once the battle started, following Hannibal's plans, the mercenaries attacked, stealing weapons and shields from their victims and causing chaos and confusion in the Roman camp.

Macrobius, citing the Roman annalist Quintus Claudius Quadrigarius, states the battle was fought ante diem iiii nones Sextilis, or 2 August.

For example, Livy records a lunar eclipse in 168 BC as occurring on 4 September, when astronomical calculations show it happened on Julian day 21 June of that year.

Their infantry comprised an estimated 8,000 Libyans, 5,500 Gaetulian, 16,000 Gauls, mainly Boii and Insubres (8,000 were left at camp the day of battle) and 8,000 of several tribes of Hispania, including Iberians, Celtiberians and Lusitanians.

[37][38] Rome's forces used typical Roman equipment including pila (heavy javelins) and hastae (thrusting spears) as weapons as well as traditional bronze helmets, bodyshields and body armor.

[42] The Numidian cavalry were very lightly equipped, lacking saddles and bridles for their horses, and wearing no armor but carrying small shields, javelins and possibly a knife or a longer blade.

The Romans followed this convention fairly closely, but chose extra depth rather than breadth for the infantry in hopes of breaking quickly through the center of Hannibal's line.

[54] This aspect of Hannibal's leadership was highlighted in the use of a Spanish unit, the Balearic slingers, whom he placed behind the infantry to hurl their ranged missiles into the masses of Roman troops.

[55] Roman sources claim their placement was chosen for being the most expendable and unreliable troops, but modern reflections believe those forces were actually selected for their battle-hardening to carry the weight of the Punic side, as they would be tasked with the controlled retreat that ultimately made possible Hannibal's pincer movement.

[64] Polybius described many of the Hispanic and Celtic horsemen facing the Romans dismounting due to the lack of space to fight on horseback, and called the struggle "barbaric" in the sense of its utter brutality.

[71] At this decisive point, Hannibal ordered his African infantry to turn inwards and advance against the Roman flanks, creating an encirclement in one of the earliest known examples of a pincer movement.

After Cannae, the Hellenistic southern provinces of Arpi, Salapia, and Uzentum, including the cities of Capua and Tarentum, two of the largest city-states in Italy, and other settlements of non-Latin origin such as Herdonia,[92] revoked their allegiance to Rome and pledged their loyalty to Hannibal.

As Livy noted, "How much more serious was the defeat of Cannae than those which preceded it, can be seen by the behavior of Rome's allies; before that fateful day, their loyalty remained unshaken, now it began to waver for the simple reason that they despaired of Roman power.

Holding his naked sword over the heads of the wavering men, Scipio is reported to have cried: I swear with all the passion in my heart that I will never desert our homeland, or permit any other citizen of Rome to leave her in the lurch.

As the historian Hans Delbrück pointed out, due to the high numbers of killed and wounded among its ranks, the Punic army was not in a condition to mount a direct assault on Rome.

Even if his army were at full strength, a successful siege of Rome would have required Hannibal to subdue a considerable part of the hinterland to cut the enemy's supplies and secure his own.

[98] Even after the tremendous losses suffered at Cannae and the defection of a number of her allies, Rome still had abundant manpower to prevent this and maintain considerable forces in Iberia, Sicily, Sardinia and elsewhere, despite Hannibal's presence in Italy.

This left them vulnerable to Hannibal's tactic of double envelopment since their inability to maneuver independently from the mass of the army made it impossible for them to counter the strategic encirclement used by the Carthaginian cavalry.

First, the Romans "articulated the phalanx, then divided it into columns, and finally split it up into a great number of small tactical bodies that were capable, now of closing together in a compact impenetrable union, now of changing the pattern with consummate flexibility, of separating one from the other and turning in this or that direction.

The culminating result of this change marked the transition from the traditional manipular system to the cohort under Gaius Marius, as the basic infantry unit of the Roman army.

[104] Hannibal's double envelopment at Cannae is often viewed as one of the greatest battlefield maneuvers in history, and is cited as the first successful use of the pincer movement within the Western world to be recorded in detail.

The notion that an entire army could be encircled and annihilated within a single stroke led to a fascination among Western generals for centuries, including Frederick the Great and Helmuth von Moltke, who attempted to create their own "Cannae".

Schlieffen believed that the "Cannae model" would continue to be applicable in maneuver warfare throughout the 20th century: A battle of annihilation can be carried out today according to the same plan devised by Hannibal in long forgotten times.

[112] Although he has no connected narrative of the battle, Plutarch provides a number of details about Cannae in his Parallel Lives, specifically the essays "Fabius" and "Aemilius Paulus".