Pharsalus: Julius Caesar’s Most Decisive Battle

Caius Julius Caesar is the famous soldier/statesman in history and was the victor of many battles. The most decisive battle he fought was against fellow Romans, under Gnaeus Pompey, at a place called Pharsalus.


At the conclusion of the conquest of Gaul, Caesar was aware that his enemies in the Roman Senate wanted to prosecute him on what he considered trumped up charges. Instead of submitting to this, he marched on Rome with his army. He crossed the Rubicon into Italy in January, 49 B.C., sparking a civil war.

Caesar’s advance on Rome went almost unopposed. In a fit of caution, Pompey, who led the armies of the Roman Senate, retreated into Greece along with much of the Senate, to raise more troops and await Caesar on a battlefield of his choosing.

This gave Caesar time to settle things in Spain in a lightening campaign against forces loyal to Pompey while consolidating his position in Rome. Then he pursued Pompey across the Adriatic, fought him and lost at Dyrrhachium, then retreated to Pharsalus. At first Pompey refused to pursue, calculating that Caesar’s lack of supplies would eventually defeat him without bloodshed. But he was finally pressured to give chase and destroy Caesar with his superior numbers.

The Battle of Pharsalus

Pharsalus took place on an open plain near the Enipeus River in Thessaly. Pompey anchored his 55,000 man army with the right flank anchored on the river and his left flank covered by cavalry. His infantry was deployed in three lines ten legionaries deep.

Caesar ‘s army was about 23,000 men deployed with the right flank anchored on the river and cavalry on the left flank. Behind the cavalry, unseen by Pompey, were 3,000 legionaries in a reserve. The rest of Caesar’s men were in three lines, similar to Pompey’s, but six deep.

Pompey’s plan was to engage Caesar’s infantry with his own while using his cavalry to sweep Caesar’s from the field before taking his enemy’s infantry in the flank and rear. However things did not proceed as planned as Caesar’s cavalry gave way and his reserve infantry advances, using javelins to stab at Pompey’s horsemen. Then it was Caesar’s cavalry and reserve infantry’s time to attack, taking Pompey army in the flank and rear and defeating it in detail.

Why Pharsalus was Decisive

If Caesar had lost at Pharsalus, he would have been killed or captured and then executed and the Roman Republic would have lived for a while longer. Since Caesar won, Pompey was obliged to flee to Egypt, where he was murdered. Caesar spent some years mopping up, but his ultimate victory in the Roman Civil War was not in doubt. Not even his assassination sufficed to save the Republic. Caesar’s great nephew Octavian, later known as Augustus, eventually prevailed over all of his rivals and established Rome as an empire ruled by one man.

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