As described in Julius Caesar's Gallic Wars, Rome had secured domination over the Celtic tribes beyond the Provincia Narbonensis (modern day Provence) through a careful Divide and rule strategy. Before, the Gallic tribes were at war with each other, but Vercingetorix managed to unify the tribes (something his father had failed to do) and adopted more modern styles of warfare. He adopted the policy of retreating to natural fortifications, and undertook an early example of a Scorched earth strategy by burning towns to prevent the Roman legions from living off the land.
Caesar and his chief lieutenant Labienus lost the initial minor engagements, but captured the tribal capital at Avaricum (Bourges), killing the entire population of 40,000. The next major battle at Gergovia resulted in a victory for Vercingetorix because Caesar was too anxious and had attacked instead of besieging and starving the city in standard Roman fashion. When Vercingetorix thought Caesar was in retreat (which he did not intend because it might have ruined his career) he abandoned the cautious tactics he had adopted before and attacked head on. Due to losses he had to retreat and moved to another stronghold, Alesia.
In the Battle of Alesia, however, Caesar was more patient and built a fortification around the city. However, because he himself was surrounded by the rest of Gaul, and Vercingetorix had summoned his Gallic allies to attack the besieging Romans, Caesar built another outer fortification against the expected relief armies (resulting in a doughnut-shaped fortification). The relief came in vast numbers, an estimated 100,000 (although Caesar claimed there were 250,000). But the tactical leader, Vercingetorix, was cut off from them on the inside and without his guidance the attacks weren't very successful at first. However, the attacks did reveal a weak point in the fortifications and the combined forces on the inside and the outside almost made a breakthrough. Only when Caesar led the last reserves into battle in person did he finally manage to prevail. This was a decisive battle in the creation of the Roman Empire.
Vercingetorix surrendered in magnificent fashion, allegedly riding his horse out of Alesia and riding around Caesar's camp before throwing his arms at Caesar's feet, then kneeling to Caesar with a flourish. He was imprisoned in the Tullianum in Rome for five years, before being publicly displayed.
He died in 46 BC, and there are two theories as to his cause of death: the first and most likely is that he was strangled shortly after Caesar's triumph in 46 BC; a second popular theory, based on legend, is that he was beheaded by Romans.