Cannae: Rome’s Darkest Hour

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“So many thousands of Romans were lying there, foot and horse promiscuously, according as accident had brought them together, either in the battle or in the flight … some too they found lying alive with their thighs and hams cut who, laying bare their necks and throats, bid their conquerors to drain the last of their blood.”

               — Livy 

Before the advent of the Early Modern Era, the Second Punic War was the most destructive conflict the world had ever seen. In the 3rd Century B.C., more than a million men were hauled into a titanic struggle for what was, in effect, hegemony of the known world. The rising Roman Republic – backed by its vast reserves of manpower, terrifying legions and dogmatic culture – locked horns with the African city of Carthage, whose only advantage was the genius of its greatest general, Hannibal Barca. That genius reached its climax at Cannae, where some 80,000 Romans faced a mere 50,000 Carthaginians, only to be deceived, encircled and utterly slaughtered. On that day, 67,500 men were killed – a number that would not be matched until the Battle of the Somme – in a battle so tactically masterful that many of history’s greatest generals have hailed it as a work of art.

Rome and Carthage (a city in modern Tunis which then dominated the North African coast) had first fought in the First Punic War. After Rome emerged from that conflict triumphant, the Carthaginian general Hamilcar Barca had made his young son Hannibal swear “never to be a friend of Rome.” As a man, Hannibal had lived up to his oath by carving out an empire for Carthage in Spain. When hostilities erupted again between Carthage and Rome, Hannibal seized the initiative and marched across the Pyrenees, Southern France and then the Alps. Most had assumed it was impossible to cross those mountains in the middle of winter; Hannibal not only summited the Alps, but did so with a herd of war elephants – though most died after the journey due to the cold weather.

The stunned Romans immediately sent an army to defeat the invader, but, at the Battle of Trebia in 218 B.C., Hannibal gained his first major victory against the Republic. He had cannily baited the rash Roman general Sempronius Longus into marching his legionaries across a freezing river early in the morning of the Winter Solstice – the coldest day of the year. There, they encountered war elephants for the first time. The terrified Roman infantrymen managed to hold their ground, but the Italian cavalry were routed by their Carthaginian counterparts, who then flanked the Roman foot-soldiers. At that moment, a squadron of Hannibal’s troops, who had hidden in a forest directly behind the Roman camp, rushed forward, assaulted the rear of Sempronius’ line and surrounded the legions. Encircled, the Roman army was crushed.

The enraged Republic sent another army to avenge the soldiers of Sempronius, this time under the equally hotheaded general Gaius Flaminius. Flaminius pursued the Carthaginian army through a narrow defile, which was bordered by Lake Trasimene on one side and a steep hill on the other. One morning, when there was a thick fog, the Roman vanguard encountered Carthaginian heavy infantry and engaged them. What Flamininus did not realise was that this force was just a fraction of Hannibal’s host, the rest of which had been hidden on the hill parallel to the defile. Suddenly, an entire Carthaginian army appeared from the mist, catching the Romans completely out of formation, unprepared and in every way unready for battle. Some legionaries tried to run back along the defile, only to find Carthaginian horsemen lying in wait. In their panic, many attempted to swim to safety, only to drown in their armour. Bottled in, a second army was cut down.

Rome now descended into a panic. Two armies had been crushed, and an enemy was roaming Italy at will. The distraught Republic took a desperate step and appointed a Dictator, an ancient office the Romans only used in their times of greatest need. A Dictator wielded absolute power for six months, in which time he was supposed to defend Rome and stabilise the situation, before surrendering his powers at the end of his term of office and restoring the traditional political order. The man the Romans awarded supreme power to was Fabius Verracosus, a statesman who had warned the Senate on the eve of war that it was fatally underestimating Carthage, and would find winning the war far more challenging than declaring it. Fabius’ advice had gone unheeded then, but, after two bloody defeats, the Senate was now willing to hear his counsel.

Fabius developed a novel strategy. He refused to directly engage Hannibal in a pitched battle, but instead wore him down with months of attritional warfare. This new way of fighting, later known as Fabian tactics, relied on defeating an enemy through cutting their supply lines, denying them the ability to forage and sapping their morale. Fabius’ efforts were certainly effective – indeed, in more recent times they have been emulated with great success by George Washington in the American Revolutionary War, by Kutosuv against Napoleon in Russia and by the Viet Minh during the First Indochina War. Hannibal’s army began to feel strain, while Rome steadily restored its strength and morale.

Yet Fabius’ strategies enraged the Romans, to whom it seemed cowardly to permit Hannibal to go about ravaging the Italian countryside unmolested. Fabius was heckled by the city he was trying to save, and Hannibal, hearing of the discontent, compounded it by ordering his soldiers not to damage the Dictator’s estates – knowing the Romans would assume the two had reached some secret deal. At the end of his six month term, Fabius stepped down as the most unpopular man in the Republic. 

As traditional politics resumed after its six month hiatus, it came time for Rome to elect its two consuls (the joint heads of state) for the following year. The ambitious politician, Marcus Terrentius Varro, ran a campaign promising to end Fabius’ craven strategies, to assemble the largest army Rome had ever fielded and to pulverise Hannibal once and for all. He won in a landslide election. Varro began training eight legions, and an equal number of Italian troops were raised. Combined with his cavalry, this amounted to a force totalling around 86,000 men and, with this gargantuan army, Varro marched to face Hannibal, whose 56,000 strong army was massively dwarfed. 

The two armies were radically different beasts. Rome has conquered Italy using a sophisticated citizen militia; soldiers were Roman citizens or the subjects of their Latin allies, and were armed according to their age and economic status. Poor teenagers served in the front line as skirmishers, young men in their twenties served as heavy infantry swordsmen and older veterans served as spearmen at the back. The flanks were defended by wings of cavalry, who were drawn from the young sons of wealthy nobles. Yet the horsemen were not an especially well-trained or well-disciplined force, and were not expected to be the instrument of victory. A legion’s power came instead from its infantry core, which could usually hack its way through an enemy line to victory. 

Hannibal’s army was structured in a radically different way. Carthage lacked the population base to field a citizen militia, and so had historically hired mercenary contingents to fight its wars for it. The core of Hannibal’s army were the Iberian soldiers from Carthage’s Spanish empire, who served both as swordsmen and as heavy cavalry. From the African continent came Numidian horsemen, who could dance around less talented riders while pelting them with javelins, and crack spearmen, Hannibal’s finest infantrymen. The Carthaginian host had also picked up many Gallic infantrymen on its journey to Italy, though these were largely undisciplined and untested, fighting mainly out of their hatred for the Republic that had encroached on their lands. 

History records that, from the outset, Varro was desperate to engage Hannibal, while his consular colleague Aemilius Paullus urged caution. How much weight should be ascribed to these accounts is debated – Polybius, the main chronicler of these events, received considerable patronage from Paullus’ grandson, and likely had little interest in tarnishing the good name of his powerful backer’s family. Nonetheless, the traditional telling of events posits that Aemilius, despite his frantic efforts, was unable to persuade Varro to show proper caution. Since supreme command of the legions alternated between the two consuls every day, Hannibal simply waited until Varro was in command and then provoked a battle.  

Fearing a repeat of the ambushes at Trebia and Trasimene, the Romans selected the wide open plain of Cannae to face Hannibal, offering the wily general no places to conceal Carthaginian contingents. The Romans attempted to play to their strengths, the greatest of which was their immense numerical superiority. The only issue posed by the vast size of the Roman force was that it made the army extremely unwieldy; no general of the Republic had experience leading so many men, and issuing orders in the heat of battle would be essentially impossible. Attempting any complex manoeuvres was likely to cause chaos, and the Roman commanders decided to adopt the simplest stratagem of all – attack.

At Cannae, Varro, Paullus and their advisors packed the Roman infantry into an extremely dense formation, sacrificing flexibility on the altar of sheer frontal power; their plan was to essentially bulldoze through the weaker Carthaginian infantry line. This strategy had several merits – the Romans knew that their heavy infantry was far superior to anything that the Carthaginians could field, and at both Trebia and Trasimene, groups of legionaries had cut their way through Hannibal’s line to escape. Once the Carthaginian infantry crumpled, their cavalry would be unable to assault the Roman legions directly, and would either flee the field or be cut down at Cannae.

Yet Hannibal had anticipated this behaviour. His greatest advantage was his cavalry; his 10,000 horsemen were both more numerous and more skilled than their Roman counterparts, and the flat plain of Cannae was ideal terrain for the riders. Hannibal ordered his infantry in an inverted crescent – such that the line’s centre was closer to the Romans than its ends were. He positioned the Gauls and Spaniards in his army’s middle, deliberately weakening it and inviting a direct attack, and ordered them not to flee before the Roman onslaught, but to steadily concede ground. Realising this would be where the fighting would be thickest, Hannibal placed himself and his brother Mago behind the Gauls and Spaniards, hoping to shame those considering flight. On either side of the Gallic-Spanish line, Hannibal placed his crack African infantry in deep columns.

On his army’s extreme flanks he placed his horsemen – with the Numidians forming up on the right and Spaniards on the left. The battle began when both wings of Carthaginian cavalry charged, and the elite Spaniards smashed through their foes with laughable ease. The Numidians were ill-suited for close quarters combat, but held their ground against their Roman foes. The Spanish cavalry rode the length of the plain of Cannae, darted behind the Roman infantry and smashed the remaining Italian cavalrymen’s rear. The Numidians were saved, and Rome’s entire cavalry force was driven from the field. In a colossal blunder, Varro and Paullus, the army’s supreme commanders, had positioned themselves with the cavalry and, accordingly, had been chased from the field at the battle’s outset. Without either general, the Romans could not redeploy or change their battle plan. Instead, they could only now rush into Hannibal’s trap.

This was precisely what they did. Seeing the inverted crescent, the heavily armed Roman centre was lured into focusing its attack on Hannibal’s Spaniards and Gauls. This attack was, at first, extremely successful, and the Romans were fooled into funnelling ever greater numbers of men into the assault until the whole army assembled at Cannae was committed. It was now that Hannibal played his masterstroke.

As ordered, the Spaniards and Gauls had been slowly falling back, meaning that the inverted crescent had righted itself to become a standard crescent – where the centre of the line lies below its ends. At this point, Hannibal ordered his elite African infantry, who had been drawn up on the ends of the Carthaginian line as a reserve and had seen little action, to redeploy. They advanced forwards, pivoted 90 degrees and then charged inwards, falling upon the Romans from both sides. The Romans were surrounded on three sides and, when the Spanish cavalry charged back into battle for the third time that day and engaged the Romans at the back of their army, the encirclement was completed. The front of the legions could make no headway against the Gallic-Spanish forces opposite them, the men on the flanks were confronted by African spearmen and those in the Roman rear were hacked down by horsemen.

What followed was sheer horror. The trapped Romans now had no way to escape their envelopment, and could only wait to be cut down where they stood. Varro’s earlier tightening of the legions meant the men were completely packed together, and had no way to redeploy – indeed, most barely had the space to raise their sword and shield. Most of the 70,000 trapped men were gruesomely killed on the field of Cannae, and the Carthaginians only started taking prisoners when their arms grew tired from the hacking. In their panic, some legionaries in the centre began digging holes in the dirt with their helmets, so they might suffocate themselves to death by burying their heads instead of facing the Carthaginians.

Only 3,400 of the Romans managed to flee, and the 10,000 troops guarding the camp near Cannae were captured immediately after the battle. Varro himself managed to escape, but his career was over and he would live out his days in inglorious ignominy. His co-consul Paullus was even less lucky – the Carthaginians had caught up with him and slain him during the battle. 

When the news of the defeat at Cannae was heard in Rome, the city was thrown into panic. The Sybilline Books (ancient Roman prophetic texts) were consulted, the Delphic Oracle was visited and four people were buried alive in an attempt to appease the gods. Yet if Cannae is the ultimate testament to what a brilliant general can achieve in battle, it is also the ultimate testament to the limits of what a single battle can achieve in a war. Rome had lost a fifth of its adult male population in a day – for comparison, Germany lost only 13% of its young men during the four years of the First World War. A defeat of this magnitude should have crippled Rome, and Hannibal sent emissaries to the Senate, expecting to negotiate a victorious peace. 

Yet following Cannae, the Romans refused to surrender, refused to negotiate peace and refused even to ransom their prisoners. Instead, the Republic steeled itself for years of war, and slowly sapped Hannibal’s strength through Fabian tactics. History would vindicate this decision; Rome still had the population reserves to continue waging war, and Hannibal stood little chance of successfully storming the city, defended as it was by colossal walls. Fourteen years after Cannae, the Roman general Scipio forced Hannibal to withdraw to Africa, decisively defeated him at the Battle of Zama and won the Second Punic War. Rome went on to enjoy a century of expansion; without a rival in Carthage, no counter-weight existed to stop the Republic becoming the master of much of the Mediterranean basin.

Dodge, T., 1891. Hannibal. War College Series

Goldsworthy, A., 2012. Cannae: Hannibal’s Greatest Victory. Basic Books

Livy., The History of Rome

Polybius, The Histories