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The battle of Pharsalus: how Julius Caesar defeated Pompey

It was the ultimate heavyweight contest – Rome’s two greatest leaders in a bloody fight to the finish. Julian Humphrys explains how Julius Caesar emerged as victor…

Pompey flees after the battle of Pharsalus
Published: August 9, 2022 at 7:00 am
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Down on paper, it looked like the battle that was about to be fought in central Greece would be an easy victory for Pompey. He had twice as many men as his enemy, seven times as many cavalry and, what’s more, his men were well fed, while those of his enemy were chronically short of supplies. There was just one problem – that enemy was Julius Caesar.

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Caesar and Pompey had once been allies, but Caesar’s stunning successes in Gaul changed that as Pompey saw his once-unrivalled prestige being eclipsed. Furthermore, many in the Roman Senate, especially the aristocratic optimate faction, saw Caesar’s growing wealth, ambition and popularity as a threat to the Republic in general, and their influence in particular. In a bid to cut him down to size, they ordered Caesar to step down from his military command. Caesar refused and, in 49 BC, in a direct challenge to the authority of the Senate, he crossed the river Rubicon into Italy with a legion of soldiers – an illegal act that led to civil war.

Battle of Pharsalus: fast facts

When was it fought?

9 August 48 BC

Where?

Pharsalus, central Greece

Who fought in the battle?

Caesar: 22,000 men, 1,000 cavalry Pompey: 45,000 men, 7,000 cavalry

Why was it fought?

Struggle for power between Caesar and Pompey

Who won?

Victory for Caesar

Within weeks he had overrun Italy, helped by the fact that Pompey, the overall commander of the forces opposed to him, had withdrawn to his power base in the east. Caesar then mopped up opposition in Spain before crossing to Macedonia in January to take on Pompey himself. After an initial defeat at Dyrrachium (in modern-day Albania), where his attempt to capture the enemy supply base ended in abject failure, Caesar moved his hungry army into central Greece and confronted Pompey near the town of Pharsalus.

Caesar leads troops across the Rubicon
When Caesar led his troops across the Rubicon into Italy, it sparked civil war. (Image by Getty Images)

Although he had twice as many men as Caesar, and a powerful cavalry force drawn from all over the Roman empire, Pompey was in no hurry to fight. Caesar was isolated in a hostile country and was desperately short of provisions, and Pompey reasoned that hunger would eventually force him to surrender. Nevertheless, pressured by his officers and the Senators that were with him, he reluctantly agreed to give battle.

Who was Pompey the Great? (106-48 BC)

During his long career, Gnaeus Pompeius Magnus (Pompey the Great) won a string of impressive military victories. He played an important part in Sulla’s victory over Marius in the Roman civil war of 82 BC, fought in Sicily, Spain and Africa, helped to stamp out the Spartacus slave revolt, cleared the Mediterranean of pirates and conquered Armenia, Syria and Palestine.

An excellent administrator, his organisation of Rome’s newly won territories in the east was a huge success. Such was his power and prestige that, in 70 BC, although well below the legal age for such a post, he was appointed consul – the highest elected political office of the Roman Republic.

The secret alliance he concluded with his rivals Julius Caesar and Marcus Crassus – cemented when he married Caesar’s daughter, Julia – initially worked well. The trio dominated Roman politics for seven years. But, when Crassus was killed, Julia died and Caesar began amassing power in Gaul, the alliance fell apart. Pompey began to see Caesar as a dangerous enemy whose power urgently needed curbing.

Surprise strategy

Both generals deployed their troops in three lines, Caesar making sure that the left flank of his army was hard up against the river Enipeus. That way it was impossible for Pompey’s fast-moving cavalry to ride around them. Realising this, Pompey massed his cavalry against Caesar’s right flank. His plan was simple – while his own infantry place, his horsemen would sweep aside the enemy’s paltry cavalry force and then wheel inwards to attack Caesar in the flank and rear.

It was a sound enough plan, but Caesar was up to the challenge. Knowing full well that it was highly likely that he’d be faced with a mass of enemy cavalry marauding around his right flank, he took steps to counter the threat. Detaching six cohorts from the legions in his third line, he formed them up in a fourth line, angled back behind his own cavalry on the right and hidden from their enemies by the horsemen in front of them. According to the Greek historian Plutarch, Caesar briefed them personally, telling them not to throw their pila at a distance but to “strike them upwards into the eyes and faces of the enemy; telling them that those fine young dancers… would fly to save their handsome faces.”

Warriors and weapons at the battle of Pharsalus

The backbone of both armies was provided by professional Italian heavy infantry. 

These were organised into ‘centuries’ of 80 men, each one commanded by a centurion who led from the front and a second-in-command called an optio, who was stationed in the rear to keep the ranks in order. Six centuries made up a cohort, and ten cohorts a legion. 

This meant that on paper, a legion consisted of 4,800 men. In practice, this was rarely the case, especially if, like Caesar’s legions at Pharsalus, they had been on campaign for some time. 

While the mocking words he used undoubtedly played on the infantryman’s traditional contempt for the pretty boys in the cavalry, the idea behind them was deadly serious. Once they’d thrown their pila, his infantry would have had to fight with their short swords and would lack the reach to defend themselves properly. But, if they held onto them, they could confront their enemies with a deadly obstacle – a wall of shields bristling with spear points.

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Their well-drilled ranks and brightly painted shields must have made an intimidating sight, as the first two lines of Caesar’s well-trained legions tramped silently and steadily towards their enemies across the dusty Greek plain. Then something unexpected happened. Although at that time it was customary for both armies contact, Pompey’s men didn’t move an inch. Caesar always considered that it was a mistake to meet a charge at the halt as advancing troops tended to be more confident and had the forward momentum, but Pompey had his reasons for ordering his men to stay where they were. He was concerned that if he ordered an advance, the inexperienced legions and the foreign allies that made up much of his army would become disorganised. By staying put they would at least maintain his enemies who would be tired and disorganised. Furthermore, by drawing Caesar’s troops onto him, Pompey would make it easier for his cavalry to ride around and encircle them.

However, Caesar’s men were seasoned professionals. When they realised that Pompey’s men weren’t going to advance to them, his legions calmly halted, drew breath, dressed their rank then moved on again. Once they were in range, they hurled their pila, drew their swords, and charged screaming at Pompey’s men, who threw their own pila and braced themselves for the impact.

One of the first to reach them was Caius Crastinus, a veteran centurion from Caesar’s tried and trusted Tenth Legion, which was stationed on the vulnerable right flank of the line. Before the battle began, he had promised Caesar that, alive or dead, he would deserve his commander’s praise by the end of the day. And he kept his word. Caesar himself later recalled that Crastinus was the first man to run forward on the right, followed by a hand-picked force of 120 volunteers. According to another account, “the army testified that he had switched from rank to rank like a man possessed.” Crastinus would earn his commander’s praise, but he didn’t survive the battle. He was eventually felled by a sword thrust that went into his mouth and came out the back of his neck.

Outnumbered seven to one

Pompey’s infantry was coming under intense pressure but, by committing his reserves, he somehow ensured that his line held firm. It was now time for his horsemen to make their move, and the air echoed to the sound of thousands of hooves as Pompey’s massed cavalry thundered forward to attack. Caesar had an extra reason to watch their advance, for they were led by Titus Labienus, his old second-in-command in Gaul who had angered him by defecting to Pompey. With an advantage in numbers of about seven to one, the result was never in doubt, and Labienus duly pushed back the Caesarean cavalry who had ridden to oppose him.

During the battle of Pharsalus, Rome’s two greatest leaders in a bloody fight to the finish
During the battle of Pharsalus, Rome’s two greatest leaders in a bloody fight to the finish. (Image by Getty Images)

But he and his men were in for a shock. As Labienus’s horsemen milled about trying to regain their order after their charge, Caesar ordered his hidden fourth line of infantry to advance. In one of the most devastating attacks ever made by infantry upon cavalry, they emerged from the clouds of dust that had hidden them from view and did as Caesar had instructed, stabbing and thrusting with their pila at Labienus’s disorganised horsemen. Taken by surprise, the cavalry panicked and stampeded to the rear, leaving the left wing of Pompey’s army completely exposed.

Peering into the dust in an attempt to see what was happening, Pompey watched with horror as first his cavalry emerged in full retreat, and then the soldiers of Caesar’s fourth line came into view as they wheeled around to attack his army in the flank. He’d already been forced to commit his reserves into the battle against Caesar’s frontal assault, so he had nothing left to counter this new threat. When Caesar finally ordered his third line to join in the attack, Pompey realised that the battle was lost. With his allies streaming back in disorder and his legions slowly but surely giving ground, he abandoned the field and rode back to the temporary safety of his fortified camp.

While Pompey sat in his tent in shattered disbelief, Caesar was busy on the battlefield, urging his men, who by now had the entire enemy army on the run, to carry on and complete their victory by capturing Pompey’s camp and the treasures and supplies it housed. As Caesar’s men drove its defenders and burstinto the camp, Pompey finally stirred. Exchanging his red general’s cloak for the clothes of a common soldier, he rode away unnoticed, accompanied by a handful of trusted advisors.

Caesar was stunned by the opulence of his enemy’s camp. “It was easy to deduce from their pursuit of inessential pleasures that they had no misgivings about the outcome of the day,” he later wrote. Meanwhile, the pursuit went on until nightfall. According to Caesar, while 15,000 of Pompey’s men were killed and a further 24,000 were taken prisoner, his own army lost just 200 rank-and file and 30 centurions. It had been a stunning victory.

What happened after the battle of Pharsalus?

After the destruction of his army at Pharsalus, Pompey fled to Egypt. If he thought that it would provide him with a secure bolthole while he rallied his supporters, he was badly mistaken. He was immediately murdered on the orders of the advisors of the young Egyptian king Ptolemy XIII, who hoped to curry favour with Caesar. The Civil War might have ended there and then but Caesar, who had followed Pompey to Egypt, spent several months in Alexandria getting involved in the dynastic struggle there and conducting a highly public affair with Cleopatra, its legendary queen.

This allowed his remaining enemies to regroup, and forced him to fight further campaigns in Africa and Spain before victory was finally won. Caesar returned to Rome, where he made himself dictator for life. But his victory was to be short-lived. On 15 March 44 BC, Caesar was assassinated by a group of disgruntled senators.

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This article first appeared in the Christmas 2016 issue of BBC History Revealed

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