Why did Caesar cross the Rubicon?

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In early January 49 B.C., Julius Caesar abandoned Cisalpine Gaul and crossed the river Rubicon, entering the province of Italy with his army and inciting a major civil war in Rome against Pompey. This move was a serious breach of all accepted Roman norms and customs and had not been attempted since the Sulla era (138-78 B.C.). So, the question that follows is what drove Caesar to such desperation that he saw fit to invade his own country?

Caesar’s decision to cross the Rubicon was predominantly for his personal interests, both self-preservation and furtherance of his political career. In 50 B.C., the Senate, supported by Caesar’s nemesis, Pompey, had ordered Caesar to disband his army and stand trial for war crimes during his conquest of Gaul. Caesar risked losing everything if he adhered to their commands, and thus he responded with by demonstrating his full military right – effectively ‘invading’ Italy with his own army.

Indeed, two prominent classical historians – Suetonious and Asinius Pollo – agree that Caesar feared likely impeachment on return to Rome. Senior optimates (traditionalist, conservative Senators who opposed Caesar), notably Milo and Cato, had pledged to prosecute Caesar once he returned to the capital. If Caesar came back to Rome without an army at his back, he risked the disintegration of his power and persecution at the hands of Pompey who had placed himself decisively into the anti-Caesarian optimate camp.

However, in his self-justifying history of the conflict, Caesar tries to reverse this narrative, instead presenting his decision to cross the Rubicon as in the interests of Italy’s population. His account claims that “all the prefectures … receive him with the utmost gladness and assist his army with supplies of every kind.” This assertion – clear Caesarian propaganda – is evidently designed to suggest that his crossing of the Rubicon was welcomed by the Italians who saw Caesar as their necessary saviour: the man who would preserve the Republic from the despotism of Pompey as sole consul (i.e., ruler of the Republic).

This assertion is contradicted by Cicero in his letter to Atticus on January 18 49, which declares, “If Pompey makes a stand in Italy we shall all be with him.” There are varying interpretations of this letter. Some have suggested that the ‘we’ refers to the general populace who would stand against Caesar and his tyranny. It is, however, far more likely that Cicero’s ‘we’ is the powerful senatorial group with which he was involved. Regardless of which interpretation is more valid, it is clear that Caesar’s invasion was not welcomed by all, and civil war was thus the likely outcome of his crossing. 

Nonetheless, Caesar remains typically unrepentant in his account of events. In addition to removing Pompey, he claims that one of his primary motives for departing Gaul was to “restore to their position the tribunes of the plebs [effectively the peoples’ champions] who at that conjuncture had been expelled from the state.” He was supposedly acting altruistically, promising temporary dictatorship for a supposed ‘greater good.’ Such a narrative is supported by a later historian, Suetonius, who reports that Caesar only intended to resort to war if the tribunes were marginalised by Pompey. War was, apparently, neither Caesar’s aim nor desire, but rather a necessary evil to remove Pompey and restore the people’s power. From this, it seems as though the primary cause of civil war was Caesar’s desire to safeguard the political powers of the populace from the optimates.

This viewpoint, espoused by both Caesar and Suetonious, is highly debatable. Caesar has an obvious bias in hoping to portray a romanticised, selfless version of his crossing of the Rubicon, whilst Suetonious can be criticised for a similar lack of objectivity. His writing takes a very favourable approach to the reigns of both Caesar and his successor Augustus, with the hope of providing a contrast to the more immoral Emperors who succeeded them. His work should thus be read cautiously, as should the idea that the Civil War arose from Caesar’s valiant defence of the plebeian class.

Hence it is clear that the crossing of the Rubicon – this hugely consequential act which started the Roman civil war – was the result of a squabble for a power among the Roman upper classes in which the plebeians were mere bystanders. For all that Caesar may have protested that he was defending the rights of the populace, in truth his thirst for power, combined with the intransigence of Pompey and the optimates, led to a rapid disintegration of the norms of the Republic and inevitable conflict. Their quarrelling would spill over into a conflict which would fuel the downfall of the Roman Republic, before the Empire rose out of its ashes.

Beard, M., 2015. SPQR: A History of Ancient Rome. Profile Books.

Cicero, edited Shackleton Bailey, D.R., 1980. Cicero: Selected Letters. Cambridge University Press.

Julius Caesar, translated Peskett, A.G., 1914. Caesar: The Civil Wars. W. Heinemann.

Rawson, E., 1975. Cicero: A Portrait. Bloomsbury.

Suetonius, translated Rolfe, J.C., 1914. Divus Julius. Harvard University Press.