Battle of Pharsalus

The Battle of Pharsalus, fought on 9 August 48 BC during Caesar’s Civil War, was the climactic confrontation between Gaius Julius Caesar and the Republican forces led by Gnaeus Pompeius Magnus (Pompey the Great). Taking place near Farsala in central Greece, it ended in an overwhelming Caesarian victory. Pompey fled to Egypt where he was assassinated on arrival, leaving Caesar the unrivalled master of the Roman world.

Background to the Campaign

Civil war broke out in 49 BC when Caesar crossed the Rubicon in defiance of senatorial orders. Pompey and the majority of the Senate withdrew from Italy, intending to regroup in the eastern provinces. By the end of 49 BC Caesar had consolidated his position in Italy and neutralised Pompeian forces in Spain.
In early 48 BC Caesar crossed the Adriatic to confront Pompey. He attempted to seize Dyrrachium but suffered a setback when Pompey broke his siege lines. Caesar withdrew into Thessaly, both to draw Pompey away from Italy and to relieve his officer Gnaeus Domitius Calvinus, threatened by Metellus Scipio arriving from Syria. Caesar stormed Gomphi to secure supplies and continued to manoeuvre in central Greece.
Pompey, under pressure from senators and eastern monarchs in his camp, was urged to deliver a decisive battle. Although initially cautious, convinced that starvation and attrition would defeat Caesar in time, he eventually accepted engagement on Thessalian plains.

The Battlefield and Its Identification

The precise location of the battlefield has been much debated. Ancient authors variously described the engagement as taking place at Pharsalus or at Palaepharsalus (Old Pharsalus). Caesar himself gave few geographical indications. Modern scholarship has increasingly supported a site north of the river Enipeus, centred on the hill east of the modern village of Krini (formerly Driskoli), near the ancient road from Larisa to Pharsalus. This identification—argued in detail by J. D. Morgan—situates Pompey’s camp west of Krini and Caesar’s several miles to the south-east, placing the battle between Old Pharsalus and the river.
The ancient distinction between Old and New Pharsalus, both associated with sanctuaries of Thetis, adds complexity, though the site near Krini appears to offer the strongest archaeological and topographical evidence.

Naming the Battle

While modern historians frequently refer to the “Battle of Pharsalus”, ancient usage was inconsistent. Caesar described it only as a battle “in Thessaly”; Cicero and Hirtius used terms such as proelium Pharsalicum. Several authors—including Strabo, Frontinus and Orosius—placed the battle at Palaepharsalus, while only a few (Plutarch, Appian, Polyaenus) explicitly used “Pharsalus”. Some scholars therefore argue that Pharsalia—the poetic form used by Lucan—may more accurately reflect its historical designation.

Opposing Forces

The strength of the armies at Pharsalus is difficult to determine, as ancient accounts emphasise Roman legionary numbers and often minimise allied contingents.
Caesar’s Army

• Around 22,000 Roman legionaries in eight understrength legions
• Reinforced by approximately 1,000 Gallic and German cavalry
• A few thousand Greek light infantry from Dolopia, Acarnania and Aetolia
• Veteran legions included VI Ferrata, VII Claudia Pia Fidelis, VIII Augusta, IX Hispania, X Equestris (Gemina), XI Claudia, XII Fulminata and XIII Gemina.Most had campaigned with Caesar in Gaul and were seasoned troops exceptionally loyal to their commander.

Pompey’s Army

• Between 36,000 and 45,000 legionaries, depending on the source
• Possibly 5,000–7,000 cavalry, vastly outnumbering Caesar’s mounted arm
• Numerous contingents of archers, slingers and light infantry
• Allies included Thracians, Greeks, Anatolians, Syrians, Phoenicians, Jews and other eastern peoples
• Many allied contingents served under the authority of eastern kings who were clients of Pompey

Pompey’s numerical superiority, particularly in cavalry, led many in his camp to believe victory was assured.

Deployment and Battle Plan

Both commanders arranged their forces in the traditional triplex acies—three lines of infantry.
Pompey anchored his right and Caesar his left on the Enipeus river, protecting that flank. Confident in his mounted superiority, Pompey placed almost all his cavalry on his left flank along with archers and slingers. Only a small detachment of around 500–600 auxiliaries held his weakened right. His objective was to overwhelm Caesar’s right, envelop his line and shatter his infantry.
Caesar anticipated this. He formed an additional fourth line of picked cohorts behind his right wing, instructed not to charge but to thrust forward with their pila at close quarters to disrupt the horsemen. Caesar then advanced slowly, halting midway to draw Pompey’s charge out of sequence and disrupt his timing.

The Battle

Pompey’s cavalry surged forward and initially pushed back Caesar’s horsemen. At this critical moment Caesar’s concealed fourth line advanced, attacking the riders with coordinated volleys. The tactic succeeded: Pompey’s cavalry recoiled in disorder and fled, leaving the archers and slingers exposed. Without their cavalry screen these troops were quickly routed.
With Pompey’s left collapsing, Caesar ordered his infantry forward. The veteran cohorts pressed against Pompey’s centre, which had been instructed to receive Caesar’s attack rather than counter-charge. The Republican line began to buckle. Caesar committed his third line fresh, tipping the balance decisively.
As his army dissolved, Pompey withdrew to his camp, despairing of the outcome. Disguised as an ordinary citizen he fled to the coast, eventually reaching Egypt, where he was murdered on the orders of Ptolemy XIII.

Aftermath and Significance

Pharsalus ended organised Republican resistance in the east. Caesar rapidly regrouped his forces, moving on to confront remaining Pompeians in Africa and Spain. Pompey’s assassination deprived the senatorial cause of its principal leader and further consolidated Caesar’s dominance.
Politically, the victory marked the decisive moment in the collapse of the late Republic. Although civil war continued for several years, the outcome at Pharsalus paved the way for Caesar’s dictatorship and ultimately the transformation of Rome into an imperial state.