A dispute between Caesar and the optimates faction in the Senate of Rome culminated in Caesar marching his army on Rome and forcing Pompey, accompanied by much of the Roman Senate, to flee from Italy to Greece in 49 BC where he could better conscript an army to face his former ally. Caesar, lacking a fleet to immediately give chase, solidified his control over the western Mediterranean – Spain specifically – before assembling ships to follow Pompey. Marcus Calpurnius Bibulus, whom Pompey had appointed to command his 600-ship fleet, set up a massive blockade to prevent Caesar from crossing to Greece and to prevent any aid to Italy. Caesar, defying convention, chose to cross the Adriatic during the winter, with only half his fleet at a time. This move surprised Bibulus and the first wave of ships managed to run the blockade easily. Now prepared, Bibulus managed to prevent any further ships from crossing, but died soon afterwards.
Caesar was now in a precarious position, holding a beachhead at Epirus with only half his army, no ability to supply his troops by sea, and limited local support, as the Greek cities were mostly loyal to Pompey. Caesar's only choice was to fortify his position, forage what supplies he could, and wait on his remaining army to attempt another crossing. Pompey by now had a massive international army; however, his troops were mostly untested raw recruits, while Caesar's troops were hardened veterans. Realizing Caesar's difficulty in keeping his troops supplied, Pompey decided to simply mirror Caesar's forces and let hunger do the fighting for him. Caesar began to despair and used every channel he could think of to pursue peace with Pompey. When this was rebuffed he made an attempt to cross back to Italy to collect his missing troops but was turned back by a storm. Finally, Mark Antony rallied the remaining forces in Italy, fought through the blockade and made the crossing, reinforcing Caesar's forces in both men and spirit. Now at full strength Caesar felt confident to take the fight to Pompey.
Pompey was camped in a strong position just south of Dyrrhachium with the sea to his back and surrounded by hills, making a direct assault impossible. Caesar ordered a wall to be built around Pompey's position in order to cut off water and pasture land for his horses. Pompey built a parallel wall and in between a kind of no man's land was created, with fighting comparable to the trench warfare of World War I. Finally the standoff was broken by a traitor in Caesar's army, who informed Pompey of a weakness in Caesar's wall. Pompey immediately exploited this information and forced Caesar's army into a full retreat, but ordered his army not to pursue, fearing Caesar's reputation for setting elaborate traps. This caused Caesar to remark, "Today the victory had been the enemy's, had there been any one among them to gain it." Pompey continued his strategy of mirroring Caesar's forces and avoiding any direct engagements. After trapping Caesar in Thessaly, the prominent senators in Pompey's camp began to argue loudly for a more decisive victory. Although Pompey was strongly against it—he wanted to surround and starve Caesar's army instead—he eventually gave in and accepted battle from Caesar on a field near Pharsalus.
The date of the actual decisive battle is given as 9 August 48 BC according to the republican calendar. According to the Julian calendar however, the date was either 29 June (according to Le Verrier's chronological reconstruction) or possibly 7 June (according to Drumann/Groebe). As Pompey was assassinated on 3 September 48 BC, the battle must have taken place in the true month of August, when the harvest was becoming ripe (or Pompey's strategy of starving Caesar would not be plausible).
The location of the battlefield was a long subject of controversy among scholars. Caesar himself, in his Commentarii de Bello Civili, mentions few place-names; and although the battle is called after Pharsalos, four ancient writers – the author of the Bellum Alexandrinum (48.1), Frontinus (Strategemata 2.3.22), Eutropius (20), and Orosius (6.15.27) – place it specifically at Palaepharsalos. Strabo in his Geographica (Γεωγραφικά) mentions both old and new Pharsaloi, and notes that the Thetideion, the temple to Thetis south of Scotoussa, was near both. In 198 BC in the Second Macedonian War Philip V of Macedon sacked Palaepharsalos (Livy, Ab Urbe Condita 32.13.9), but left new Pharsalos untouched. These two details perhaps imply that the two cities were not close neighbours. Until the early 20th century, unsure of the site of Palaepharsalos, scholars followed Appian (2.75) and located the battle of 48 BC south of the Enipeus or close to Pharsalos (today's Pharsala).
The “north-bank” thesis of F. L. Lucas, based on his 1921 solo field-trip to Thessaly, is now, however, broadly accepted by historians. “A visit to the ground has only confirmed me,” Lucas wrote in 1921; “and it was interesting to find that Mr. Apostolides, son of the large local landowner, the hospitality of whose farm at Tekés I enjoyed, was convinced too that the [battle-]site was by Driskole [now Krini], for the very sound reason that neither the hills nor the river further east suit Caesar’s description.” John D. Morgan in his definitive “Palae-pharsalus – the Battle and the Town”, arguing for a site closer still to Krini, where he places Palaepharsalos, writes: “My reconstruction is similar to Lucas’s, and in fact I borrow one of his alternatives for the line of the Pompeian retreat. Lucas’s theory has been subjected to many criticisms, but has remained essentially unshaken.”
Caesar had the following legions with him:Legions of veterans from the Gallic Wars – Caesar's favourite legion, X Equestris, and those later known with the names of VIII Augusta, IX Hispana, and XII Fulminata
Legions levied for the civil war – legions later known as I Germanica, III Gallica, and IV Macedonica
However, all of these legions were understrength. Some only had about a thousand men at the time of Pharsalus, due partly to losses at Dyrrhachium and partly to Caesar's wish to rapidly advance with a picked body as opposed to a ponderous movement with a large army. According to his accounts, he had 80 cohorts on the battlefield, about 22,000 men.
In total, Caesar counted 110 complete cohorts in the Pompeian army, 11 legions consisting of about 45,000 men, although Orosius, following Livy and Pollio, only counted 88 cohorts, and Hans Delbrück suggests that Caesar's count includes detachments at Dyrrachium and elsewhere, leaving only 88 cohorts in the Pompeian army.
Pompey deployed his infantry in the traditional three lines of 10 men deep, on the Pharsalian plain, in the following order: Legions I and III on the left with Pompey himself stationed here. At his center were the legions from Syria commanded by Scipio, and on his right, against the Enipeus River, were legions from Cilicia and Spanish auxiliaries. Pompey's cavalry, which greatly outnumbered Caesar's, were commanded by Caesar's old lieutenant during the Gallic Wars and brilliant cavalry commander Labienus. He massed them into a single body on his left flank together with his auxiliary archers and slingers. Pompey's tactical plan was to allow Caesar's legions to charge while his own stood their ground; reasoning that the enemy would fatigue by charging double distance and that his own men would better withstand the pilum toss while stationary. Simultaneously his cavalry would overwhelm the enemy's and then take the legions in the flank and rear — a classic hammer and anvil tactic.
Caesar also deployed his men in three lines, but, being outnumbered, had to thin his ranks to a depth of only six men, in order to match the frontage presented by Pompey. His left flank, resting on the Enipeus River, consisted of his battle worn IXth legion supplemented by the VIIIth legion, these commanded by Mark Antony. The center was commanded by Domitius and upon his right he placed his favored Xth legion, giving Sulla command of this flank — Caesar himself took his stand on the right, across from Pompey. Upon seeing the dispositions of Pompey's army, Caesar grew discomforted and further thinned his third line in order to form a fourth line on his right. This to counter the onslaught of the enemy cavalry, which he knew his numerically inferior cavalry could not withstand. This new line he gave detailed instructions for the role they would play, hinting that upon them would rest the fortunes of the day, and gave strict orders to his third line not to charge until specifically ordered.
There was significant distance between the two armies, according to Caesar. Pompey ordered his men not to charge, but to wait until Caesar's legions came into close quarters; Pompey's adviser Caius Triarius believed that Caesar's infantry would be fatigued and fall into disorder if they were forced to cover twice the expected distance of a battle march. Also stationary troops were expected to be able to defend better against pila throws. Seeing that Pompey's army was not advancing, Caesar's infantry under Mark Antony and Gnaeus Domitius Calvinus started the advance. As Caesar's men reached near throwing distance, without orders, they stopped to rest and regroup before continuing the charge; Pompey's right and centre line held as the two armies collided.
As Pompey's infantry fought, Labienus ordered the Pompeian cavalry on his left flank to attack Caesar's cavalry; as expected they successfully pushed back Caesar's cavalry, Caesar then revealed his hidden fourth line of infantry and surprised Pompey's cavalry charge, Caesar's men were ordered to leap up and use their pila to thrust at Pompey's cavalry instead of throwing them. Pompey's cavalry panicked and suffered hundreds of casualties. After failing to reform, the rest of the cavalry retreated to the hills, leaving the left wing of Pompey's legions exposed. Caesar then ordered in his third line, containing his most battle-hardened veterans. These broke Pompey's left wing troops, and they fled the battlefield.
After routing Pompey's cavalry, Caesar threw in his last line of reserves —a move which at this point meant that the battle was more or less decided. Pompey lost the will to fight as he watched both his cavalry and legions under his command break formation and flee from battle, he retreated to his camp and left the rest of his troops at the centre and right flank to their own devices, ordering the garrisoned auxiliaries to defend camp as he gathered his family, loaded up gold, and threw off his general's cloak to make a quick escape. As the rest of Pompey's army were left confused, Caesar urged his men to end the day by routing the rest of Pompey's troops and capturing the Pompeian camp. They complied with his wishes; after finishing off the remains of Pompey's men, they furiously attacked the camp walls. The Thracians and the other auxiliaries who were left in the Pompeian camp, in total seven cohorts, defended bravely, but were not able to fend off the assault.
Caesar had won his greatest victory, claiming to have only lost about 200 soldiers and 30 centurions. In his history of the war, Caesar would praise his own men's discipline and experience, and remembered each of his centurions by name. He also questioned Pompey's decision not to charge.
Pompey fled from Pharsalus to Egypt, where he was assassinated on the order of Pharaoh Ptolemy XIII. Ptolemy XIII sent Pompey's head to Caesar in an effort to win his favor, but instead secured him as a furious enemy. Ptolemy, advised by his regent, the eunuch Pothinus, and his rhetoric tutor Theodotus of Chios, had failed to take into account that Caesar was granting amnesty to a great number of those of the senatorial faction in their defeat. Even men who had been bitter enemies were allowed not only to return to Rome but to assume their previous positions in Roman society.
Pompey's assassination had deprived Caesar of his ultimate public relations moment — pardoning his most ardent rival. The Battle of Pharsalus ended the wars of the First Triumvirate. The Roman Civil War, however, was not ended. Pompey's two sons, Gnaeus Pompeius and Sextus Pompey, and the Pompeian faction, led now by Metellus Scipio and Cato, survived and fought for their cause in the name of Pompey the Great. Caesar spent the next few years 'mopping up' remnants of the senatorial faction. After seemingly destroying all his enemies and bringing peace to Rome he was assassinated by friends in a conspiracy organized by Marcus Junius Brutus and Gaius Cassius Longinus.
Paul K. Davis wrote that "Caesar's victory took him to the pinnacle of power, effectively ending the Republic." The battle itself did not end the civil war but it was decisive and gave Caesar a much needed boost in legitimacy. Until then much of the Roman world outside Italy supported Pompey and his allies due to the extensive list of clients he held in all corners of the Republic. After Pompey's defeat former allies began to align themselves with Caesar as some came to believe the gods favored him, while for others it was simple self-preservation. The ancients took great stock in success as a sign of favoritism by the gods. This is especially true of success in the face of almost certain defeat — as Caesar experienced at Pharsalus. This allowed Caesar to parlay this single victory into a huge network of willing clients to better secure his hold over power and force the Optimates into near exile in search for allies to continue the fight against Caesar.
The battle gives its name to the following artistic, geographical, and business concerns:Pharsalia, a poem by Lucan
Pharsalia, New York, U.S.
Pharsalia Technologies, Inc.