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The Road to Pharsalus

When the war began, Caesar was a rebel with no navy and three understrength legions, while Pompey was backed by all the resources of the Roman state and his clients in the East. However, his position was weaker than it seemed, since he was simply an advisor to the Senate, many of whose members either preferred a negotiated solution, or regarded him with as much suspicion as Caesar. His military strategy had to be approved by the consuls, and he could only issue recommendations, which were not always followed. For example, Cicero rejected a request to help him with recruitment, and Cato refused to take command of Sicily, vital for control of Rome's grain supply.

Plans to defend Italy were undone by the speed with which Caesar moved, advancing directly on Rome with minimal resistance. Although outnumbered, his troops were experienced veterans, while many of Pompey's were new recruits, a weakness made worse by lack of co-ordination. Cato's brother-in-law, the optimate leader Lucius Domitius, was cut off and captured in a hopeless defence of Corfinium, and his 13,000 men incorporated into Caesar's army. Led by Asinius Pollio, they were later used to occupy Sicily.

Pompey had abandoned Rome, ordering all senators and public officials to accompany him as he withdrew south to Brundisium. From there, he transported his troops across the Adriatic to Dyrrhachium in Thessaly, an operation performed with almost complete success. Lacking ships to pursue him, Caesar first secured his rear by subduing Pompeian forces in Hispania, before returning to Rome in December 49 BC. This gave Pompey time to build an army nearly twice the size of his opponents, while his navy destroyed two fleets being built for Caesar, ensuring the Pompeians retained control of the sea lanes.

Despite this, in January 48 BC Caesar managed to cross the Adriatic with seven legions and land in southern Albania. After capturing Oricum and Apollonia, he advanced on Pompey's main supply base at Dyrrhachium. The latter arrived in time to block the attempt, and establish a fortified camp on the other side of the River Apus, where the two armies remained until spring. Neither commander was anxious to begin hostilities, since Caesar was too weak militarily, while as with Mithridates, Pompey preferred to starve his opponent into submission.

In late March the stalemate was broken when Mark Antony finally managed to cross the Adriatic with four more legions and land at Nymphaeum, some 57 kilometres north of Dyrrachium. Pompey tried to prevent the two Caesarian armies from linking up, by marching north-east and laying an ambush for Antony. The ambush, however, was revealed to Antony by some local Caesarian sympathisers, and he stayed in camp until Caesar approached. Pompey not willing to be caught between the two Caesarian forces withdrew.

Caesar, his army now united with Antony's force, redeployed his forces by sending one-and-a-half legion to win support and gather supplies in Aetolia and Thessaly, and a further two legions under Domitius Calvinus to intercept Metellus Scipio in Macedonia. Meanwhile, Gnaeus, Pompey's oldest son, managed to destroy Caesar's fleet at Oricum and Lissus, making sure no more reinforcements and supplies would reach Caesar from Italy. Caesar tried to lure Pompey into a pitched battle at Asparagium, but the latter refused. The next day Caesar outmaneuvred Pompey and marched for Dyrrachium again. When Pompey arrived at the city Caesar had already set up camp.

Caesar lacked the siege equipment needed to take Dyrrhachium, and could not risk leaving Pompey to threaten his rear. He solved this by besieging Pompey in his camp. Although the latter had enough food, water was scarce because Caesar had dammed the local rivers, and the Pompeian cavalry lacked forage for their horses. Ending the stalemate became a matter of urgency, and in late July Pompey finally managed to break through part of Caesar's defensive lines. Since this made the blockade pointless, Caesar cut his losses and withdrew to Apollonia.

At this point Metellus Scipio arrived in Thessaly. Caesar moved south to confront this threat and link up with Domitius Calvinus, allowing his men to sack Gomphi en route. Pursued by Pompey, he then withdrew to the area near Pharsalus, but failed to tempt Pompey into giving battle. Although it was later claimed Pompey only did so after being pressured by his subordinates, the delay may simply have been a reflection of his natural caution.

Regardless, Pompey's army of around 38,000 outnumbered the 22,000 men commanded by Caesar, with 7,000 cavalry to 1,000. On 9 August he deployed his men in battle formation, planning to use his superior cavalry to outflank his opponent on his left. Caesar had anticipated this, and repulsed the cavalry which fled in confusion, exposing the infantry behind them. Under pressure from the left and in front, the Pompeian army collapsed.