The Civil War of Caesar and Pompey

Civil War of Julius Caesar and Pompey the Great was one of the most pivotal conflicts in Roman history, marking the end of the Roman Republic and the rise of imperial rule. Fought from 49 BCE to 45 BCE, this war stemmed from intense political rivalry, personal ambition, and the breakdown of the First Triumvirate—a political alliance between Caesar, Pompey, and Crassus. As Caesar’s power grew through his conquests in Gaul, the Senate, aligned with Pompey, viewed him as a threat to the Republic. When Caesar crossed the Rubicon River in 49 BCE with his army—a direct challenge to Roman law—civil war erupted. The struggle culminated in decisive battles, most notably at Pharsalus in 48 BCE, where Caesar defeated Pompey. This war ultimately reshaped Rome’s political landscape and set the stage for the emergence of the Roman Empire under Caesar and, later, Augustus.

The Civil War of Caesar and Pompey

The Civil War of Caesar and Pompey

Introduction

The Civil War between Julius Caesar and Pompey the Great was a defining moment in Roman history that led to the fall of the Roman Republic and the rise of autocratic rule. Taking place from 49 BCE to 45 BCE, the conflict was rooted in a power struggle between two of Rome’s most prominent leaders. After the death of Crassus, the alliance known as the First Triumvirate dissolved, and tensions between Caesar and Pompey intensified. The Senate, fearful of Caesar’s growing popularity and military strength, sided with Pompey and ordered Caesar to relinquish his command. Instead, Caesar famously crossed the Rubicon River, declaring, “Alea iacta est” (“The die is cast”), and initiated a civil war. The conflict spanned multiple regions—from Italy to Greece to Egypt—and resulted in Caesar’s ultimate victory and the consolidation of his power. This war marked a turning point in Roman politics, ending centuries of republican governance and laying the foundation for the Roman Empire.

Three-person alliance

The political careers of Marius and Sulla, as well as Catilina, show the increased level of competition in the late Republic and the ruthlessness with which some Roman politicians in the period attempted to gain the consulship. In 60 BCE, however, a group of three politicians tried to achieve its goals by doing something atypical of Roman politicians who had largely only looked out for themselves: the three formed an alliance in order to help each other. Spectacularly, their alliance even transcended the usual division of Populares and Optimates, showing that, for these three men at least, the thirst for political power was more important than any other personal convictions.

Magnus or The Great

Marcus Licinius Crassus was the wealthiest man in Rome, son of a consul, and consul himself in 70 BCE. His colleague in the consulship in 70 BCE, Gnaeus Pompey, achieved military fame in his youth, earning him the nickname “Magnus,” or “the Great,” from Sulla himself.

Secret alliance

By 60 BCE, however, both Crassus and Pompey felt frustrated with their political careers so joined forces with a relative newcomer to the world of politics, Gaius Julius Caesar. The three men formed their alliance, secret at first, an alliance which Cicero later dubbed the Triumvirate. To cement the alliance, Caesar’s daughter, Julia, married Pompey. Together, they lobbied to help each other rise again to the consulship and achieve desirable military commands.

The worst laws in Roman history

The alliance paid immediate dividends for Caesar, who was promptly elected consul for 59 BCE and was then awarded Gaul as his province for five years after the consulship. Crassus and Pompey, in the meanwhile, were re-elected consuls for 55 BCE, and, in the same year, Caesar’s command in Gaul was renewed for another five years. One modern historian has called it “the worst piece of legislation in Roman history,” since the renewal did not specify whether the five-year clock started afresh in 55 BCE—in which case, Caesar’s command was to end in 50 BCE—or if the five years were added to the original five-year term—in which case, Caesar’s command would have ended in 48 BCE.

Caesar’s popularity

A talented writer, as well as skilled general, Caesar made sure to publish an account of his Gallic campaigns in installments during his time in Gaul. As a result, Romans were continually aware of Caesar’s successes, and his popularity actually grew in his absence. His rising popularity was a source of frustration for the other two triumvirs. Finally, the already uneasy alliance disintegrated in 53 BCE. First, Julia died in childbirth, and her baby died with her. In the same year, Crassus was killed at the Battle of Carrhae, fighting the Parthians. With the death of both Julia and Crassus, no links were left connecting Caesar and Pompey; the two former family relations, albeit by marriage, swiftly became official enemies.

The beginning of the civil war

Late in 50 BCE, the Senate, under the leadership of Pompey, informed Caesar that his command had expired and demanded that he surrender his army. Caesar, however, refused to return to Rome as a private citizen, demanding to be allowed to stand for the consulship in absentia. When his demands were refused, on January 10th of 49 BCE, Caesar and his army crossed the Rubicon, a river which marked the border of his province. By leaving his province with his army against the wishes of the Senate, Caesar committed an act of treason, as defined in Roman law; the civil war began.

Battle of Pharsalus

While most of the Senate was on Pompey’s side, Caesar started the war with a distinct advantage: his troops had just spent a larger part of a decade fighting with him in Gaul; many of Pompey’s army, on the other hand, was disorganized. As a result, for much of 49 BCE, Pompey retreated to the south of Italy, with Caesar in pursuit. Finally, in late 48 BCE, the two fought a decisive battle at Pharsalus in northern Greece. There, Caesar’s army managed to defeat Pompey’s much larger forces. After the defeat, Pompey fled to Egypt, where he was assassinated by order of Ptolemy XIII, who had hoped to win Caesar’s favor by this action. When he arrived in Egypt in pursuit of Pompey, Caesar, however, sided with Ptolemy’s sister Cleopatra VII and appears to have fathered a son with her, Caesarion.

End of the civil war

With Pompey’s death, the civil war was largely over, although Caesar still fought a number of battles across the Roman world with the remnants of the senatorial army. It is indeed striking to look at a map of Caesar’s military career. While his military actions on behalf of Rome were largely limited to Gaul, with a couple of forays into Britain, his civil war against Pompey and his allies took Caesar all over the Roman world from 49 to 45 BCE.

Conclusion

The Civil War between Julius Caesar and Pompey was more than a personal rivalry—it was a decisive turning point in Roman history that signaled the collapse of the Republic and the rise of centralized imperial power. Caesar’s victory not only eliminated his most powerful rival but also dismantled the traditional republican institutions that had governed Rome for centuries. After defeating Pompey and his allies, Caesar emerged as the unchallenged leader of Rome, setting in motion reforms and consolidating authority that would ultimately lead to his dictatorship. Although his assassination in 44 BCE briefly interrupted this shift, the Republic never recovered. The civil war’s long-term consequence was the end of republican rule and the birth of the Roman Empire under Caesar’s heir, Augustus. The war fundamentally reshaped Rome’s political landscape and marked the beginning of a new era in world history.

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