Julius Caesar, after a series of victories at Vellaunodunum, Genabum, and Noviodunum, had arrived at Avaricum in the winter of 52 BC, intent on denying its grain and steel to the rebellious Gauls. Vercingetorix, aware that he had been already been bested three times, decided to change tactics. Calling together a council of the tribes in rebellion against Rome, he convinced them to adopt Fabian strategy, never offering combat with Caesar's forces, and denying them supplies. All the towns within range of Caesar's foraging parties were destroyed, the land stripped bare, and all grain removed or burned. However, Avaricum was spared this fate since the Biturges argued the town was impossible to take, and Vercingetorix agreed to make the town an exception.
However, upon Caesar's appearance at the gates of Avaricum, Vercingetorix moved his army to a distance fifteen miles outside town, perfectly situated so Caesar could not leave without a battle, nor could he forage at will. To add to his woes, Caesar's allies, the Aedui and the Boii, were unable to supply him, the former because they had quietly joined Vercingetorix in his rebellion, the latter because they simply did not have any food to spare. The shortage of grain was so acute that the men ate meat, despite the fact that they did not really enjoy it. Caesar personally made the rounds amongst his men, telling them that if the scarcity of food was too much, he would lift the siege and withdraw. His soldiers protested, refusing to end a siege in disgrace when they still had to avenge the innocent Romans murdered by the Gauls.
Contented by this, Caesar designed and began engineering an impressive siege apparatus. Starting from high ground, he built a siege terrace of sorts. Two flanking walls were made, along with two towers to be advanced fully made. Another wall was built between the flanking walls to connect them and open the front for the battle.
As construction on Caesar's siege terrace continued, Vercingetorix moved his cavalry into a camp closer to Caesar's, intent on ambushing Caesar's foraging troops. Having discovered this, Caesar countered, marching in the dead of night and threatening Vercingetorix's main camp. This drew Vercingetorix back to his main camp, rushing to its aid. His aim accomplished, Caesar withdrew.
After twenty-five grueling days of construction, and contending with Gallic raids and attempts to set the whole siege terrace on fire, Caesar's apparatus was completed. Caesar ordered the towers advanced, and much to his good fortune, a fierce storm struck, driving the Gallic sentries to seek cover rather than stand watch. Taking advantage of this lack of discipline, Caesar stealthily moved his soldiers into the towers and the wall, and launched a brutal strike. The walls fell quickly, and the surviving Gauls retreated to the center of town, forming a wedge formation, determined to fight to the end. However, no Roman legionary descended from the walls, simply stood at their ease, watching the Gauls. Panic struck the Gallic defenders, and they all fled for wherever they thought there was an avenue of escape.
However, Caesar's legions were in no mood to spare any of the forty thousand Gauls within Avaricum, especially after twenty five days of short rations and great frustration. Only eight hundred managed to escape the massacre that followed. After feeding and resting his men at Avaricum until the beginning of June, Caesar moved on Gergovia, determined to draw Vercingetorix into battle in a campaign that would eventually culminate in the Battle of Alesia.