49f Julius Caesar crossed the RubiconRiver

Crossing the Rubicon

On 10 January 49 BC, leading one legion, the Legio XIII Gemina, General Julius Caesar crossed the RubiconRiver, 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 acoup d'état; thus, Caesar's military action began a civil war.

This act of war on the Roman Republic by Caesar led to widespread approval amongst the Roman civilians, who regarded him as a hero. The historical records differ about which decisive comment Caesar made on crossing the Rubicon: one report is Alea iacta est (usually translated as "The die is cast")

Caesar's March on Rome was a triumphal progress; yet, the Senate, ignorant of Caesar's being armed only with a single legion, feared the worst and supported Pompey, who, on grasping the Republic's endangerment, said: "Rome cannot be defended", and escaped to Capua with his politicians, the aristocratic Optimates and the regnant consuls; Cicero later characterised Pompey's "outward sign of weakness" as allowing Caesar's politico-military consolidation to achieve Roman dictatorship.

Despite having retreated, in central Italy, Pompey and the Senatorial forces disposed of at least two legions, some 11,500 soldiers (he earlier had ordered Caesar return to Italy from Gaul), and some hastily levied Italian troops commanded by Lucius Domitius Ahenobarbus (Domitius). As Caesar progressed southwards, Pompey retreated towardsBrundisium, initially ordering Domitius (engaged in raising troops in Etruria) to stop Caesar's movement on Rome from the direction of the Adriatic seaboard.

Belatedly, Pompey ordered Domitius to retreat south also, and make junction with Pompey's forces. Domitius mostly ignored Pompey's orders, and, after being isolated and trapped near Corfinium was forced to surrender almost thirty cohorts of troops (about three Legions), most of whom promptly joined Caesar's army.

Pompey escaped to Brundisium, there awaiting sea transport for his legions, to Epirus, in the Republic's eastern Greek provinces, expecting his influence to yield money and armies for a maritime blockade of Italy proper. Meanwhile, the aristocrats (the Optimates)—including Metellus Scipio and Cato the Younger—joined Pompey there, whilst leaving a rear guard at Capua.

Caesar pursued Pompey to Brundisium, expecting restoration of their alliance of ten years prior; to wit, throughout the Great Roman Civil War's early stages, Caesar frequently proposed to Pompey that they, both generals, sheathe their swords. Pompey refused, legalistically arguing that Caesar was his subordinate and thus was obligated to cease campaigning and dismiss his armies before any negotiation. As the Senate's chosen commander, and with the backing of at least one of the current consuls, Pompey commanded legitimacy, whereas Caesar's military crossing of the Rubicon River frontier rendered him a de jure enemy of the Senate and People of Rome. Nevertheless, in March 49 BC, Pompey escaped Caesar at Brundisium, fleeing by sea to Epirus, in Roman Greece.

Taking advantage of Pompey's absence from the Italian mainland, Caesar effected an astonishingly fast 27-day, north-bound forced march to destroy, in the Battle of Ilerda, Hispania's politically leader-less Pompeian army, commanded by the legates, Lucius Afranius (Afranius) and Marcus Petreius (Petreius), afterwards pacifying Roman Hispania; in campaign, the Caesarian forces—six legions, 3,000 cavalry (Gallic campaign veterans), and Caesar's 900-horse personal bodyguard—suffered 70 men killed in action, while the Pompeian forces lost 200 men killed and 600 wounded.

Returned to Rome in December of 49 BC, Caesar was appointed Dictator, with Mark Antony as his Master of the Horse. Caesar kept his dictatorship for eleven days, tenure sufficient to win him a second term as consul with Publius Servilius Vatia Isauricus as his colleague. Afterwards, Caesar renewed pursuit of Pompey, then in Roman Greece.