Why Was the Battle of Pharsalus so Significant? | History Hit

Why Was the Battle of Pharsalus so Significant?

Tom Ames

09 Aug 2019

It was one of the most remarkable military achievements in Roman history. On 9 August 48 BC Gaius Julius Caesar, despite being significantly outnumbered, decisively defeated the forces of Gnaeus Pompeius Magnus and his conservative Optimate supporters.

The Battle of Pharsalus paved the way for Caesar’s rise to supremacy. Caesar and Pompey were fighting over the future of Rome, and the winner of the battle would control Rome’s mighty empire.

Caesar and Pompey

Several years before the Battle of Pharsalus the Roman Republic had been controlled by three men: Caesar, Pompey and Crassus. All three were wealthy and powerful politicians, sharing power in a system known as the Triumvirate. Pompey had even married Caesar’s daughter Julia to help cement the alliance between them.

Bust of Julius Caesar.

The Triumvirate broke down after Crassus was killed at the Battle of Carrhae and Julia died. Pompey and the Senate soon became fearful of Caesar’s power, popularity and wealth. Caesar’s political capital reached its peak after his success in conquering Gaul.

The Senate and Pompey, increasingly concerned about Caesar’s reputation among the people and lust for power, demanded that Caesar’s armies disband. His elite legions had served for nearly a decade in Gaul fighting the barbarian tribes. They were battle-hardened and fiercely loyal to Caesar owing to the money and glory he provided them.

Caesar refused to break up his military, and a civil war between him and Pompey began to seem possible. Pompey was as well-regarded a general as Caesar, and the Senate were confident he would protect Rome. This war would dictate the future of the Roman Empire: the winner would have control over Rome’s military, the provinces and the Senate.

Historian and archaeologist Simon Elliott answers the key questions surrounding one of history's most compelling figures - Julius Caesar.
Watch Now

Background to the battle

In January 49 BC Caesar and his legions crossed the Rubicon river into Italy. Entering Italy with a Roman army was considered by the Senate to be treasonous and a declaration of war. The shocked Senate, led by Pompey, lacked the soldiers to prevent Caesar taking control of Rome; they had not been prepared for him to take such drastic action.

As Caesar marched towards Rome, Pompey convinced the Senate that the best course of action would be to retreat across the Adriatic and rally legions in Greece. They did so, while Caesar prepared a fleet to transport his legions and pursue them.

In Greece, Pompey mustered a huge army from the Roman soldiers posted around the provinces, and used his fleet to blockade Italy and prevent Caesar crossing the sea. Caesar and one of his generals, Marcus Antonius, succeeded in evading Pompey’s ships and landed some of their legions in Greece, ready to take the fight to Pompey.

Bust of Pompey.

Trench warfare

Caesar and Antonius marched an under-strength army to Pompey’s fortified encampment. To prevent Pompey’s troops accessing food and water Caesar ordered his legionaries to build a long wall around Pompey’s camp. Pompey responded by building a parallel wall facing Caesar’s, but he lacked the resources to feed his besieged army for long.

Fighting began to break out between the two entrenched positions. However, these skirmishes in the no-man’s-land between the opposing walls did not yield an advantage for either general.

Before long Pompey was becoming desperate for supplies. Fortunately, luck was on his side: two Gallic noblemen serving in Caesar’s cavalry were caught stealing pay. They defected to Pompey to avoid prosecution and revealed to him the weakest point in Caesar’s lines, right where his wall touched the sea.

Pompey seized the opportunity. He sent his legions to attack the wall from the front while his auxiliaries flanked around Caesar’s wall on the seaward side. His assault was a great success and Caesar was forced into a retreat.

Pompey feared that Caesar might have set the whole incident up as a trap, so did not give pursuit. This mistake led Caesar to remark,

“Today the victory would have been the enemy’s, had there been any one among them to gain it”.

Tristan Hughes investigates the evidence for Boudica’s bloody revolt, found under modern Colchester.
Watch Now

The Battle of Pharsalus

A few weeks after Caesar withdrew from Pompey’s camp, the two generals clashed at Pharsalus. Caesar had only 22,000 men, whereas Pompey’s army was closer to 40,000. Although Caesar’s troops were more experienced, Pompey had a significant cavalry advantage.

Pompey hoped to use his cavalry to overpower Caesar’s horsemen and flank Caesar’s infantry in a ‘hammer and anvil’ manoeuvre. He was not concerned about his own legions owing to their significant numerical advantage over the enemy.

Caesar was aware of his vulnerability and used his tactical expertise to outwit Pompey. To ambush his enemy’s superior cavalry, Caesar hid a line of infantry behind his own horsemen. When the armies clashed and Caesar’s horsemen were pushed back, these infantry leapt up and charged Pompey’s cavalry, using their pila (javelins) as spears.

Pompey’s horsemen were panicked by this surprise attack and fled. Caesar then ordered his veteran legions to press forward and used his cavalry to push on Pompey’s flank. Pompey’s legions broke and ran, and Pompey fled; first from Pharsalus, then from Greece.

A tactical map depicting the decisive action on the right of the battle at Pharsalus in 48 BC.


Pompey soon arrived in Egypt where he was executed by Ptolemy XIII, who hoped to gain favour with Caesar and his allies.

Caesar, meanwhile, granted amnesty to many of the senators who had fought against him and held control over much of the Roman empire. Although there were pockets of resistance still to be crushed, Pharsalus had removed his most powerful military and political rival.

Caesar could now embark on a series of reforms which solidified his power. He established the basis for one-man rule in Rome, which his adopted son Octavian would see through to its conclusion when he became Rome’s first emperor.

The Assassination of Julius Caesar.

Four years later, shortly after being named Dictator for Life, Caesar was assassinated by some of the men he had spared after Pharsalus. He bled to death at the foot of Pompey’s statue.

Featured Image: Statue of Julius Caesar. Leomudde / Commons.

Tags: Julius Caesar

Tom Ames