Crossing the Rubicon
After Caesar spent 51 BC and the better part of 50 BC touring his newly conquered province of Gaul, political chaos was developing back in Rome.
The optimates despised Caesar and his conquests (viewing much of his campaigning as unwarranted and illegal) and looked for every opportunity to strip him of his command. These conquests not only brought in a great number of slaves, but brought so much monetary wealth into Rome, that the value of gold was actually reduced by as much as a quarter or even a third of its value before the wars.
Though the common people noticed little effect, and seemingly loved Caesar, the optimates had a great deal to lose from this devaluation of their wealth. That was only one small piece of the puzzle however. Caesar's original Consulship in 59 BC was one in which he not only thwarted optimate interests, but pushed forward a populares agenda that not only made life miserable for the conservatives, but generally rejected the law and political custom. Such actions were destabilizing and dangerous for the health of the Republican system.
They wanted to prosecute Caesar for a variety of reasons, including conducting an illegal war into Germania that the Senate had never authorized. In fact, many argued that the protection of Cisalpine Gaul and Narbonensis didn't require the war that Caesar conducted in the larger part of Gaul in the first place. Prosecuting Caesar, whether the goal was death, exile or just a symbolic limitation of his power, would prevent his re-establishment of the populares agenda that he so masterfully manipulated previously.
The years 50 and 49 BC were pivotal because during this timeframe, Caesar's 'imperium' or safety from prosecution was set to expire. Caesar badly desired the ability to run for the Consulship in abstentia, thereby allowing him the safe transfer of protection from his Proconsular Imperium, granted by his command in Gaul, to that of the actual Consulship once again.
By this time however, Pompey, likely the only man able to smooth things over, had clearly sided with the optimates. His jealously over Caesar's success and his ultimate goal of acceptance and power within the Senate took him ever further from the alliance with Caesar.
The Lex Pompeia De Magistratibus that was passed while Pompey was Consul without colleague forced a candidate to be present in Rome to run for office, and of course, one couldn't legally bring their legions to Rome for protection. Marcus Claudius Marcellus, Consul for 51 BC, tried to have Caesar recalled from his command prior to its actual legal expiration, and in 50 BC, his cousin Gaius Claudius Marcellus attempted to do the same. Caesar's only hope in Rome from a legal standpoint was the intervention of the Tribunes of the Plebes, who managed to veto any attempts to bring Caesar to his knees.
The situation continued in a virtual stalemate, with neither side willing to budge on their legal standpoints. More optimate officials were elected in 50 BC to take office for 49 BC, but Caesar still managed to hold ground. His legate Marcus Antonius was elected as Tribune for the same year, and a former opponent, Gaius Scribonius Curio was also elected but paid handsomely to side with Caesar.
The year 49 BC was shaping up to be yet another stalemate politically for Caesar, but he was quite simply running out of time. Already, in the autumn of 50 BC, in an effort to weaken Caesar, the Senate asked both he and Pompey to give up one legion each (Pompey had his armies in Spain) to secure the east against Parthia. In a wise move, the Senate boldly stripped Caesar of two legions though, one of his own, and one that Pompey had lent Caesar several years earlier during the Gallic revolt. Caesar was left with eight legions, and the legions that he had given up were never sent to Parthia. They stayed in Italy and were given to Pompey in a shrewd move that strengthened Pompey whilst weakening Caesar.
By late 50 BC, various attempts were made by the Consul Marcellus to stifle Caesar's tribunes and allow some measures of anti-Caesarean policy to go through. Curio, however, turned the tables and forced a unique vote to the senate floor. On 1st December 50 BC, Curio proposed a motion that would force both Pompey and Caesar to simultaneously lay down their commands, and the motion was passed 370 votes to 22. Though the Senate vote indicated that civil war was trying to be avoided, the hatred and/or political fear of Caesar simply couldn't be compromised.
The following day, before the measure could even be brought to Caesar, Consuls Gaius Claudius Marcellus and Lucius Cornelius Lentulus Crus ignored the Senate vote. In what was certainly an illegal action, in an era filled with political illegalities, the consuls ordered Pompey to take up command of the local legions and to raise more in defense of Rome against Caesar. The people of Rome (via the tribunes) were ignored and even the Senate in this case, though it's assured that the optimates played a major part. Certainly fearing the worst, Cicero tried to counteract this measure and avert what appeared to be a growing danger of civil war. He met with and attempted to influence Pompey into working for a compromise, but Pompey refused. Meanwhile, Caesar waited in Gaul.
Though Caesar held Rome in a precarious position by the strength of his army and the continuation of his political agenda, the Senate must hold some blame for pushing a known radical into a no-win situation. Caesar's options in these later developments were either to surrender willingly and face certain prosecution (though the outcome of such prosecution could certainly have gone either way as Caesar did have plenty of support.. and money), or go to war.
Caesar clearly had ambition that exceeded the standard, and faced with personal ruin and disgrace versus the potential disaster that a civil war could cause the Roman state, Caesar obviously chose his own status above that of the eternal city. Despite this, he began to behave rather conciliatory, perhaps sensing the dire circumstances.
After having essentially been declared war on by the Senate, he attempted to offer a compromise. First he asked to be allowed to maintain his governorship of Cisalpine Gaul and two legions, or Illyricum and only one legion, until such time as he could be elected Consul and enter Rome free from fear of prosecution. The Senate didn't act on this measure at all, though it was probably hotly debated.
Without getting a response, Caesar decided to offer the same measure that already passed the Senate just a month earlier. Curio, in late December, offered that Caesar would agree to the original proposal that both he and Pompey dismiss their armies simultaneously. This time though, there was great debate and the Senate was divided on the issue. Whether certain members of the Senate did not really desire peace, were prepared to risk war in order to defeat Caesar, or were naive enough to think that war could be averted by threatening Caesar is not entirely certain, but perhaps they simply felt that Rome would hold the loyalty of the people and that Pompey would ultimately crush Caesar if war could not be avoided.
On 1st January 49 BC and the days immediately following, the Senate rejected Caesar's final peace proposal and declared him hostis (public enemy). Caesar would have to give up his command completely or face war. The Tribunes attempted to block the measure through the people once again, but this time the Senate was entrenched. Much like Caesar, they too threw constitutionality to the wind and ignored the Tribunes, using physical violence to stop their objections.
Around the 10th January 49 BC, word reached Caesar and he marched south with the XIII Legion from Ravenna towards the southern limit of Cisalpine Gaul's border. He likely arrived around January 11, and stopped on the northern bank of the small river border, the Rubicon.
Caesar seemed to contemplate the situation understandably for some time before making his final fateful decision. First testing the loyalty of his men, (he only had the XIII legion with him at this point) he gave a stirring speech pointing out the wrongs done to him (and the tribunes).
With the clear support of his men, Caesar added, "Even yet we may draw back; but once across that little bridge, and the whole issue is with the sword." He is then reported to have muttered the now infamous phrase, from the work of the poet Menander, "Alea iacta est", quoted as "Let the die be cast" or "Let the dice fly high." The Rubicon was crossed and Caesar officially invaded the legal border from his province into Italy, thus starting the civil war.
Quickly taking several northern towns, the news reached Rome by January 17. Pompey, the Republic's hope, was left without his main army, which was still in Spain, and his support base was in the eastern provinces. Despite having two legions to Caesar's one, Caesar's Gallic legions were on the move to join him, so Pompey and the rest of Caesar's opposition had little choice but to leave Rome immediately and abandon Italy to Caesar.
Caesar's Civil War
When Caesar crossed the Rubicon, the Senate finally realized that they had made a terrible mistake. The mistake wasn't in letting the situation get that far, but in that they believed the Roman and Italian people would rally to defend the Republican system. What they failed to understand was that the people had little trust in the Senate, and that Caesar had won them over through his popular agenda while in political office.
Caesar's great propaganda campaign, his books "Bellum Gallicum (the Gallic Wars)" endeared the people even more to their almost mythical hero, and the Senate's cause in Italy was lost. Unable to levy armies, or develop a meaningful resistance, the Senate and Pompey had little choice but to take their business out of Rome and into Greece. It was here, and further east, where Pompey held considerable sway, and where the Senate hoped to raise armies to defeat Caesar.
This too, however, worked in Caesar's favor. Without the fear of bloodshed and damage to their homes in Italy, the people had little reason to support the Senate. Caesar marched throughout northern Italy accepting the capitulation of cities and garnering support with little difficulty.
Pompey and the Republicans, meanwhile, fled to Brundisium in the heel of Italy, where they hoped to secure the bulk of the transport vessels available in the region. The majority of Pompey's forces were removed across the Adriatic to Dyrrhachium, along with the bulk of the Senate, but by early March of 49 BC he still had nearly two full legions with him in Brundisium.
Caesar approached quickly with six legions in an attempt to put an end to the resistance then and there. Attempting to box Pompey in, Caesar tried to negotiate peace, but Pompey delayed just long enough to make good his escape. Despite Caesar's attempts to block the harbor, the Republicans controlled the navy and Pompey escaped with his forces intact.
Caesar now faced an important choice. Without transports, he would have to face a difficult crossing in order to pursue Pompey, and Pompey's large army of seven legions waited without their commander in Spain. He also needed to go to Rome to settle a situation that was certainly bordering on riotous. Though Caesar so far had shown clemency to his opponents, people in Rome weren't sure if the new conqueror would be like Sulla and Marius.
To complicate matters further, Caesar's Legate Titus Labienus, who was left in command of Cisalpine Gaul, decided to switch sides and support Pompey. Caesar decided the best course of action was to settle matters in Rome, then move north to deal with Labienus, and then west to confront Pompey's army in Spain. His legate Curio was sent to Sicily with three legions where the ultra-conservative Cato was governor, to not only stamp out resistance, but to secure its valuable grain supplies. Cato fled to Africa, angry at Pompey for abandoning Rome, Italy and Sicily without a fight and certainly because of the hated Caesar's success. Caesar sent another legate, Valerius, with one legion to secure Sardinia.
With the immediate neighboring provinces handled, Caesar moved on towards Rome, but first held a meeting with Cicero in Formiae. Caesar attempted to have the great orator join him in Rome to help legitimize his new government. Despite the consternation of Cicero against his 'optimate' friends, he still maintained more common ground with them and refused without certain conditions. Caesar, against Cicero's proposed solutions, agreed that it would be best to part ways, but certainly lamented the inability to secure Cicero's support.
Continuing towards Rome, Caesar arrived at the end of March, 49 BC, for the first time in 9 years. This visit however was short-lived. Aside from securing the treasury for his own war efforts - an incredible total of 15,000 bars of gold, 30,000 bars of silver and 30 million sesterces which the Republicans had neglected to secure in their haste to leave - Caesar spent less than a week in the eternal city.
In early April, Caesar prepared to march for Spain saying, "I go to meet an army without a leader, and I shall return to meet a leader without an army."