|This article covers a war or battle
Caesar's Civil War was a major military conflict in Italy between the force of the Roman Republic, led by the Consul Gnaeus Pompeius Magnus, against the rebel legions of Gaius Julius Caesar, although later historians have viewed it solely as a conflict between the two military commanders and their respective factions over control of Roman society.
Prelude to War
Caesar’s Civil War resulted from the long political subversion of the Roman Government’s institutions, begun with the career of Tiberius Gracchus, continuing with the Marian reforms of the legions, the bloody dictatorship of Lucius Cornelius Sulla, and completed by the First Triumvirate over Rome.
The First Triumvirate (so denominated by Cicero), comprising Julius Caesar, Crassus, and Pompey, ascended to power with Caesar’s election as consul, in 59 BC. The First Triumvirate was unofficial, a political alliance the substance of which was Pompey’s military might, Caesar’s political influence, and Crassus’ money. The alliance was further consolidated by Pompey’s marriage to Julia, daughter of Caesar, in 59 BC. At the conclusion of Caesar’s first consulship, the Senate (rather than granting him a provincial governorship) tasked him with watching over the Roman forests. This job, specially-created by his Senate enemies, was meant to occupy him without giving him command of armies, or garnering him wealth and fame. Caesar, with the help of Pompey and Crassus, evaded the Senate's decrees by legislation passed through the popular assemblies. By these acts, Caesar was promoted to Roman Governor of Illyricum and Cisalpine Gaul. Transalpine Gaul (southern France) was added later. The various governorships gave Caesar command of an army of four legions. The term of his proconsulship, and thus his immunity from prosecution, was set at five years, rather than the customary one year.
In 52 BC, at the First Triumvirate’s end, the Roman Senate supported Pompey as sole consul; meanwhile, Caesar had become a military hero and champion of the people. Knowing he hoped to become consul when his governorship expired, the Senate, politically fearful of him, ordered he resign command of his army. In December of 50 BC, Caesar wrote to the Senate agreeing to resign his military command if Pompey followed suit. Offended, the Senate demanded he immediately disband his army, or be declared an enemy of the people — an illegal political bill, for he was entitled to keep his army until his term expired. A secondary reason for Caesar’s immediate want for another consulship was delaying the inevitable senatorial prosecutions awaiting him upon retirement as governor of Illyricum and Gaul. These potential prosecutions were based upon alleged irregularities occurred in his consulship and war crimes committed in his Gallic campaigns. Moreover, Caesar loyalists, the tribunes Mark Antony and Quintus Cassius Longinus, vetoed the bill, and were quickly expelled from the Senate. They then joined Caesar, who had assembled his army, whom he asked for military support against the Senate; agreeing, his army called for action.
In 50 BC, at his Proconsular term’s expiry, the Pompey-led Senate ordered Caesar’s return to Rome and the disbanding of his army, and forbade his standing for election in absentia for a second consulship; because of that, Caesar thought he would be prosecuted and rendered politically marginal if he entered Rome without consular immunity or his army — to wit, Pompey accused him of insubordination and treason.
Crossing of the Rubicon
On 10 January 49 BC, leading one legion, the Legio XIII Gemina, General Julius Caesar crossed the Rubicon River, the boundary between the Cisalpine Gaul province, to the north, and Italy proper, to the south, a legally-proscribed action forbidden to any army-leading general. The proscription protected the Roman Republic from an internal military threat ; thus, Caesar's military action began a civil war. This act of war on the Roman Republic by Caesar generated significant support amongst the Roman civilians, who believed him a hero despite his recent defeat in Vercintegorix's Revolt. The historical record differs about which decisive comment Caesar made on crossing the Rubicon — one report is Alea iacta est (usually translated as "The die is cast").
Battle of Volsnii and Death of Caesar
Caesar's March on Rome was intended to be triumphal, despite the fact that in the past year most of his conquests had fallen. However, when the senate learned of Caesar's crossing of the Rubicon, they believed that Caesar's intent was to seize the city and declare himself dictator, in a manner similar to Cornelius Sulla's earlier takeover of Rome. In a panic, they turned to Pompey and his legions for assistance. Pompey alone at the time commanded two legions in Rome; some 11, 500 of the most elite Roman soldiers. Pompey and his senate allies, who had levied additional troops for him to command, was unaware that Caesar commanded only one legion. Pompey, despite calls by his supporters to retreat and leave Rome to Caesar, took his legions into Etruria, with the intent to defeating Caesar's army in the field.
Caesar's army won the first skirmish against Pompey's forces, but after Caesar's scouts confirmed that Caesar was outnumbered, he retreated into central Etruria. Caesar called for his Gallic legions to assist him, despite the ever present threat of the Arverni-led Gauls of Vercingetorix. In the meantime, he fortified the city of Volsnii, sacrificing his mobility for a fortress, and attempted to negotiate with Pompey for a renewal of their alliance and an end to the conflict. Pompey's response is not recorded by history, but it resulted in him laying siege to the city. Caesar's cavalry, his major advantage over Pompey, was useless in this situation, which damaged his forces significantly. Pompey's army eventually managed to tunnel under Caesar's wall, which they then caused to collapse by destroying their own earthworks. Although Caesar's troops inflicted massive casualties, they were eventually overwhelmed by Pompey's forces and the city fell. Julius Caesar and his cavalry attempted to break out of the city in the last moments of the siege. Pompey, who possibly overestimated Caesar's martial prowess, had his archers fire en masse into Caesar's charge, decimating it. Caesar was killed quickly into the fighting, when his horse was killed beneath him and he was thrown headfirst into the ground.
Surrender of Mark Antony
Caesar's death shocked and dismayed the Gallic Legions of Caesar's supporters, which were at the time en route to Volsnii. Caesar's lieutenants switched their allegiance to Mark Antony, who although a competent military commander himself was devastated by Caesar's death. Mark Antony submitted his surrender to Pompey nearly immediately after Caesar's death, on the condition that his life and the lives of his soldiers be spared. Pompey, who was loath to lose the support of the senate by shedding more Roman blood then was necessary, agreed. Mark Antony was allowed to live but was banished to the city of Tunis, where he lived out his life as a minor official. The legions of Julius Caesar were forcibly disbanded and dispatched to numerous lands throughout the Republic. It was hoped that if the soldiers were kept divided, they would not be able to rise to seek vengeance for their leader.
Only one of Caesar's lieutenants resisted Mark Antony's call for surrender. Marcus Brutus took a century of his elite extraordinary cavalry and drove towards Rome. However, he was assassinated by one of his lieutenants before he could reach combat, and this attack was aborted.
With the death of Caesar and the disbandment of his legions, and hope of reconquering Gaul vanished at the end of the civil war. Indeed, the Republic would have little to do with Gaul for the next two centuries, beyond formally recognizing the Kingdom of Arveri.
Pompey was now the uncontested ruler of Rome. Pompey forced the senate to declare him Dictator for a period of five years; during this time, he decimated the political elite and replaced the Tribunes with his own appointed officers. Pompey effectively ruled Rome as its sole consul until his death in 41 BC.