The Battle of Dyrrachium: How Caesar almost lost the Civil War against Pompey

The rivalry between Caesar and Pompey escalated after years in which political tension eroded important alliances and altered long-standing loyalties within the Roman Republic.

Caesar’s decision to cross the Rubicon River in 49 BCE was a direct challenge to the Senate’s authority and had begun a full-scale civil war.

This openly defied an order to disband his army, and it had positioned him as an enemy of the state in the eyes of Pompey and the senatorial elite. 

Their personal relationship had deteriorated after the death of Crassus and the breakdown of the First Triumvirate, which had once balanced their political aims.

Pompey, who was now aligned with the Senate, had abandoned Italy and had sailed to Greece, where he could draw on loyal provinces and prepare a larger army.

After he had secured control over Rome and had defeated Pompeian forces in Spain, Caesar turned his attention eastward, knowing that the war’s outcome would be decided by a direct confrontation between himself and Pompey. 

Caesar was aware that Pompey was gathering his forces in the eastern provinces, so acted quickly to launch a crossing of the Adriatic during the winter of 48 BCE.

He set sail from Brundisium with only part of his army and very limited supplies, and he relied on speed and surprise to land before Pompey could block him with his superior fleet.

The ships, vulnerable to storms and enemy patrols, managed to deposit Caesar near the mouth of the Apsus River, south of Dyrrachium, in the region of modern-day Albania. 

Marcus Antonius remained in Italy with the remainder of the legions, including two fully equipped cohorts, although he did not bring the bulk of the siege materials.

However, foul weather and control of the sea had prevented his immediate departure.

During this period of separation, Caesar’s troops lived under constant threat of attack, with no access to secure supply lines or reinforcements.

For several weeks, they endured hunger and illness that steadily eroded morale while they held their position in hostile territory.

Only after Antonius managed a narrow escape and joined Caesar across the sea did the two halves of the army reunite, although the delay had already created serious supply problems. 

Caesar found himself in a region that did not support his cause and lacked reliable provisions.

While his men had extensive combat experience, they had landed in new terrain that helped Pompey’s defensive strategies.

The city of Dyrrachium was located on the coast and protected by strong fortifications, which offered Pompey both a secure base and a reliable supply route through his naval control of the Adriatic.

His fleetm commanded in part by Libo and Bibulus, kept up a blockade that hindered Caesar’s ability to receive reinforcements. 

When he realised that he could not beat Pompey in open battle, Caesar attempted a more unusual plan.

He had built a massive network of trenches, walls, and camps in an effort to encircle the city and starve Pompey’s army into surrender.

Ancient sources claimed that these fortifications stretched approximately 15 Roman miles, or about 22 kilometres.

This approach depended on cutting off sea access, which Caesar could not do, and relied on a long siege that strained his own supply situation.

With food running low and no clear means of resupply, Caesar’s own position became increasingly unsustainable. 

Searches for food failed to meet the army’s needs, and disease began to spread through the camps.

The soldiers, many of whom had followed Caesar since the Gallic Wars, retained loyalty but struggled with physical exhaustion.

Caesar’s hopes that Pompey would be forced into a desperate breakout faded as weeks passed without the expected collapse of morale or discipline inside the city.

Instead, it was Caesar’s lines that began to buckle under pressure. 

Pompey had chosen his position carefully and refused to gamble on an early battle.

He remained behind Dyrrachium’s walls and strengthened his fortifications, which denied Caesar the opportunity to exploit weaknesses through rapid assault.

His engineers constructed outer defences, observation towers, and counter-trenches to blunt Caesar’s attempts at a total blockade, which enabled Pompey to hold the initiative without risking a full engagement. 

Meanwhile, naval superiority gave Pompey the clear logistical advantage. His ships had transported grain, weapons, and reinforcements from provinces as far away as Asia Minor, allowing him to maintain an effective siege defence.

From his fortified camps, he launched limited skirmishes and occasional raids against Caesar’s lines, which tested for weaknesses and forced Caesar to stretch his forces thin.

At every stage, Pompey acted methodically, aiming to exhaust Caesar’s resources rather than defeat him in a single blow. 

Despite calls from some of his officers to pursue a more aggressive course, Pompey remained committed to a defensive strategy that made use of his advantages in numbers and supply.

He had over twice as many troops (with some estimates placing his force at around 45,000 infantry and 7,000 cavalry) while Caesar, after the arrival of Antonius, likely commanded closer to 22,000 men.

Pompey had better provisions and secure communications with friendly cities across the region.

Caesar, in contrast, had to fight without control of the sea, without local allies, and without enough grain to maintain his lines indefinitely. 

Caesar’s attempt to reverse the situation through direct action had proved disastrous.

Because he believed he had identified a vulnerable point in Pompey’s outer defences, he had ordered an assault in July 48 BCE on a segment of wall near the sea.

His troops advanced under heavy missile fire and quickly met fierce resistance.

Pompey, having reinforced the position in anticipation of an attack, countered with cavalry and reserves who overwhelmed Caesar’s men and drove them back. 

During the retreat, panic spread through the soldiers, and several units collapsed under pressure.

Many soldiers died as they attempted to escape, and others abandoned their positions.

The defeat caused serious harm to morale and to Caesar’s reputation as a commander who rarely lost a battle.

In that moment, Caesar admitted in his writings that the enemy had secured the advantage, paraphrased by later historians as "The enemy would have won, if only they had a commander who knew how to win."

The failure not only exposed weaknesses in his tactics but also showed how far Caesar had overestimated his ability to control events on the ground. 

His siege lines were already weakened by hunger and illness, but now stood exposed to new attacks.

Pompey had the opportunity to pursue the retreating forces and potentially destroy the entire Caesarian army.

However, he chose instead to strengthen his position and reoccupy the lost fortifications.

This delay, noted by ancient sources such as Plutarch and Appian, allowed Caesar time to regroup and plan a withdrawal before total collapse. 

The battle near Dyrrachium was one of the lowest points in Caesar’s military career.

His strategy had relied too heavily on the assumption that Pompey would either break under pressure or offer battle under unfavourable conditions.

Neither occurred. The attempt to surround a larger, better-supplied enemy without naval control or reliable provisions was a strategic mistake that placed his men in extreme danger.

The assault on Pompey’s fortifications failed, and the losses suffered damaged both the army's fighting ability and the confidence of his legions. 

Logistically, Caesar’s forces could no longer maintain their position along the siege line.

Enemy raids grew more frequent, and starvation loomed. When he recognised the danger, Caesar abandoned the blockade and led his army inland into Thessaly, where he hoped to draw Pompey into a more favourable engagement.

When he chose to retreat, Caesar preserved his army but conceded the battle. His reputation for invincibility had been shaken, and his survival depended on future success. 

However, Pompey did not pursue immediately because he believed that Caesar had already suffered too much to remain a serious threat.

This mistake gave Caesar the breathing space he needed. Within a month, the two armies met again on the plains near Pharsalus on 9 August 48 BCE.

There, Caesar would regain the upper hand, but the defeat at Dyrrachium remained a reminder of how vulnerable he had been when the conditions favoured his opponent.

The failure was genuine, even though it did not prove final. But, Dyrrachium showed that Caesar could certainly lose.