Siege of Alesia — Caesar's Greatest Engineering Triumph
After the defeat at Gergovia, Vercingetorix withdrew his forces to Alesia — a hilltop oppidum in Burgundy, roughly where Dijon is today. Caesar followed and immediately began encircling the hill. The circumvallation (inner wall facing Alesia) was 18 kilometres long, studded with 23 redoubts and towers, with ditches in front. Behind it Caesar built a contravallation (outer wall) 21 kilometres long facing outward, against the expected relief army. The entire system was built in 6 weeks by perhaps 40,000 soldiers. The Gauls inside and outside attacked simultaneously on multiple occasions. The critical assault came when the relief army under Vercassivellaunus — Vercingetorix's cousin — found a weakness in Caesar's lines where the outer wall ran over a hill. At the moment of crisis Caesar appeared personally in a scarlet cloak at exactly the threatened point, rallying his men. A cavalry charge around the exterior of his own fortifications caught the relief army in the flank. The relief army dissolved. Vercingetorix rode out the next morning in his finest armour, circled Caesar's tribunal, dismounted, and surrendered his sword. He was imprisoned in Rome for six years, then strangled after Caesar's triumph in 46 BCE.
- Year: 52 BCE
- Category: Military
