On 10 January 49 BC, Roman general Julius Caesar defied an ultimatum set to him by the Senate. If he brought his veteran armies across the river Rubicon in northern Italy, the Republic would be in a state of civil war.
Fully aware of the momentous nature of his decision, Caesar ignored the warning and began to march south on Rome. To this day, the phrase “to cross the Rubicon” means to undertake an action so decisive that there can be no turning back.
The civil war that followed this decision is seen by historians as the inevitable culmination of a movement that had begun decades prior.
The crumbling of the Republic
Since the celebrated general (and major influence on Caesar) Gaius Marius had reformed the Roman legions along more professional lines by paying them himself, soldiers had increasingly owed their loyalty to their generals rather than the more abstract idea of a citizen republic.
As a result, powerful men became more powerful still by fielding their own private armies, and the last troubled years of the Republic had already seen the Senate’s power crumble in the face of the ambition of Marius, and his rival Sulla.
The pair were followed by the still-more formidable Pompey and Caesar. Before his military exploits in Gaul, Caesar was very much the junior of the two, and only rose to prominence when elected consul in 59 BC. As consul, this ambitious man of a minor noble family allied himself with the great general Pompey and the rich politician Crassus to form the First Triumvirate.
Caesar in Gaul
These powerful men had little need of the senate, and in 58 BC Caesar used their influence to secure a command in the Alps which, by giving him years of freedom and 20,000 men to command, broke every law of the Senate.
Caesar used the following five years to become one of the most brilliant and successful commanders in history. The huge, multi-racial and famously fearsome territory of Gaul (modern France) was conquered and subdued in one of the most complete conquests in history.
In his reflections on the campaign, Caesar later boasted that he had killed a million Gauls, enslaved a million more, and left only the remaining million untouched.
Caesar made sure that detailed and partisan accounts of his exploits made it back to Rome, where they made him the darling of the people in a city beset by infighting in his absence. The Senate had never ordered or even authorized Caesar to attack Gaul, but were wary of his popularity and extended his command by another five years when it ended in 53 BC.
When Crassus died in 54 BC, the Senate turned to Pompey as the only man strong enough to withstand Caesar, who now controlled huge swathes of land in the north without any senate support.
While Caesar mopped up his remaining foes, Pompey ruled as sole consul – which made him a dictator in all but name. He too was a famously brilliant commander, but was now ageing while Caesar’s star was in the ascendancy. Jealousy and fear, combined with the death of his wife – who was also his Caesar’s daughter – meant that their formal alliance broke down during the latter’s long absence.
‘The die is cast’
In 50 BC, Caesar was ordered to disband his army and return to Rome, where he was banned from running for a second consulship and would be on trial for treason and war crimes following his unlicensed conquests.
With this in mind, it is hardly surprising that the proud and ambitious general, who knew that he enjoyed the adulation of the people, decided to cross the river Rubicon with his armies on the 10 January 49 BC.
The gamble paid off. After years of war in Rome and across the provinces on a scale never before seen, Caesar was victorious and ruled supreme in Rome, with Pompey now dead and forgotten.
Without any remaining enemies, Caesar was made dictator for life, a move which culminated in his assassination by a group of senators in 44 BC. The tide could not be turned back however. Caesar’s adopted son Octavian would complete his father’s work, becoming the first true Roman Emperor as Augustus in 27 BC.