Battle of Alesia , (52 bce), Roman military blockade of Alesia , a city in eastern Gaul , during the Gallic Wars . Roman forces under the command of Julius Caesar besieged Alesia, within which sheltered the Gallic general Vercingetorix and his massive host. Caesar directed his troops to erect a series of extensive fortifications , including two walls encircling the city, to keep the defenders in and potential reinforcements out. Vercingetorix’s resistance and eventual surrender marked the final major military engagement of the Gallic Wars, securing Roman authority over Gaul in its entirety.

Beginning in 58 bce, Julius Caesar waged two military campaigns and suppressed a widespread revolt in an attempt to conquer and pacify the tribes of Gaul. However, in the early months of 52 bce, Vercingetorix of the Arverni inspired a second insurrection and rallied together a large number of tribes. Several conflicts resulted in the Roman sacking of Avaricum , a major Gallic city belonging to the Bituriges . Caesar later attempted to take Gergovia, a city controlled by the Arverni, but his army was rebuffed. The Romans thus abandoned their assault and marched south toward Cisalpine Gaul with their 10 remaining legions , summoning 10,000 auxiliaries from Germania to form an estimated total of 60,000 soldiers. During this time, representatives from all but three Gallic tribes convened at Bibracte and elected Vercingetorix as general of their unified forces. He levied troops from each of them and dispatched his cavalry to attack Caesar’s column, but the Gauls were thoroughly routed. As a result, Vercingetorix retreated with some 80,000 soldiers to the fortified town of Alesia, which belonged to the Mandubii.

Siege and battle

Upon pursuing Vercingetorix’s army to the outskirts of Alesia, Caesar observed that the town was situated atop a hill with rivers on either side; the Gauls had dug trenches and erected a stone wall around the settlement. Caesar determined that Alesia could only be taken by siege and ordered his men to encircle the perimeter of the town with a line of circumvallation spanning approximately 11 Roman miles (16.7 km) that included 23 redoubts manned by sentinels and night watches.

Vercingetorix had accumulated barely 30 days of rations, so under cover of night he sent the remainder of his cavalry through the incomplete Roman fortifications to levy a relief force from the rest of Gaul. After learning of this plan from captives, Caesar reinforced his fortifications with a wide range of obstacles and traps designed to slow any large or sudden advances. To repel an external army, he directed his troops to construct a line of contravallation that was 3 miles (4.6 km) from the first and 14 miles (21.3 km) in length. Once complete, these siege works would protect the Romans from Gallic defenders and reinforcements alike.

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In the meantime, the Gallic cavalry that had departed from Alesia succeeded in their task, having amassed a host numbering nearly 250,000 men. The Gauls appointed four generals over this army: Commius of the Atrebates, Viridomarus and Eporedirix of the Aedui, and Vercassivellaunus of the Arverni. This force thus set out to break the siege. But the Alesian defenders, having heard nothing from the relief force and growing anxious about their situation, expelled those unfit for battle from the town. The women and children of the Mandubii were sent to the Roman encampment to offer themselves for enslavement in exchange for food, but Caesar refused them.

When the Gallic host were in sight of Alesia, they set up camp a short distance from the outer wall and assumed an offensive position. Vercingetorix and his men could see them from their hilltop and prepared for a sally. The following day, both armies advanced on the Romans, but the legionaries and German auxiliaries fought from noon to sunset and drove them back. On the second day, the Gauls attempted another assault on the Roman encampment, but the external army fell upon the siege works and retreated after many casualties; having received notice of their retreat, Vercingetorix’s forces fell back to Alesia. On the third day, Gallic scouts reported the presence of a gap in the outer wall on account of a steep hill. Vercassivellaunus led 60,000 soldiers through that gap and overcame the Roman fortifications. At the same time, Vercingetorix’s soldiers attempted to force their way over the inner wall on all sides. Caesar directed reinforcements to these areas, but, upon realizing the precariousness of their situation, he personally led four cohorts and a contingent of cavalry to circumvent the outer wall and attack Vercassivellaunus’s army from behind. The Gauls in this section were quickly routed and cut down by the Roman cavalry; Vercassivellaunus himself was taken alive. The defenders of the city saw this disaster from their perch and called their soldiers back from the field. Those Gauls who survived the slaughter at the outer wall returned to their camp, causing the rest of the Gallic host to flee. That night the Roman cavalry attacked their rear, killing or capturing the remaining warriors.

On the next day, envoys from Alesia informed Caesar that Vercingetorix had convened the Gallic leaders so that they could decide how to proceed, whether they wished to execute or surrender him. Caesar demanded that they lay down their arms. The chieftains met him at the front of his camp, surrendered their weapons, and delivered Vercingetorix unto him. Having captured Alesia, Caesar gave one captive to each of his surviving soldiers as a reward.

The fall of Alesia did not mark the end of the Gallic Wars, but it was their final major conflict. Roman forces continued to eliminate remaining insurgent pockets for the next two summers, thus securing the whole of Gaul for the republic. As leader of this revolt, Vercingetorix was sent to Rome in chains, and the Senate honoured Caesar with a 20-day supplicatio for his successes in the field.