Pharsalus 48 BC: Caesar's Hidden Fourth Line Routs Pompey's Cavalry

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By summer 48 BC Julius Caesar was the one in trouble. His blockade of Pompey at Dyrrachium had collapsed, and he retreated into Thessaly, sacking Gomphi to feed his men. Pompey planned to starve him out, but the optimates in his camp, already dividing future offices, shamed him into battle. Near the Enipeus River, Pompey fielded about 45,000 infantry, modern estimates 36,000 to 38,000, in roughly 110 cohorts plus 5,000 to 7,000 cavalry. Caesar had about 22,000 infantry and 1,000 horse. Pompey massed his cavalry, archers and slingers on his open left under Labienus and stacked his infantry ten deep.

Caesar thinned his lines to six deep, pulled veterans from his third line to form a hidden fourth line behind his right, and held back the rest until he raised a flag. On Gaius Triarius' advice Pompey's infantry stood still, but Caesar's veterans halted midway to catch their breath and reform. When Labienus charged, the fourth line thrust their pila at riders' faces, the cavalry fled, and the Pompeian left was rolled up. Pompey retreated to camp, shed his commander's cloak and escaped. Appian estimates 1,200 Caesarian dead against 6,000 Pompeians and 24,000 captured. Caesar burned Pompey's letters unread and pardoned Marcus Junius Brutus, while Pompey was assassinated in Egypt on the orders of Ptolemy XIII.

• The Roman calendar was so far out of step that the August 9 battle was fought in early summer heat.
• Pompey's army drew Greeks, Thracians, Anatolians, Syrians, Phoenicians and Jews, plus riders conscripted from his own slaves.
• Caesar later criticized the order to stand still, writing that a charge fires up the men.
• Caesar claimed only 200 soldiers and 30 centurions lost against 15,000 Pompeians.
• Ancient authors called the site Palaepharsalus, an area linked to Phthia, legendary homeland of Achilles.