Battle of Alesia
Caesar engaged in the Gallic Wars (58–50 BC), which led to his conquest of Gaul beyond Gallia Narbonensis. When the Helvetii, a federation of tribes from what is now Switzerland, planned a migration to the Atlantic coast through Gaul, Caesar went to Geneva and forbade the Helvetii to move into Gaul. While he went to Gallia Cisalpina to collect three other legions, the Helvetii attacked the territories of the Aedui, Ambarri, and Allobroges, three Gallic tribes, which called for Caesar’s help. Caesar and his Gallic allies defeated the Helvetii. The Gallic tribes then asked for Caesar to intervene against an invasion by the Suebi, a Germanic tribe. Caesar defeated the Suebi. In 57 BC he intervened in intra-Gallic conflicts and marched on the Belgae of northern Gaul. From then on he conquered the Gallic peoples one by one. His successes in Gaul brought Caesar political prestige in Rome and great wealth through the spoils of wars and the sale of war captives as slaves.
Julius Caesar
Though the Gallic tribes were just as strong as the Romans militarily, the internal division among the Gauls guaranteed an easy victory for Caesar. Vercingetorix's attempt in 52 BC to unite them against Roman invasion came too late. He proved an astute commander, defeating Caesar in several engagements, but Caesar's elaborate siege-works at the Battle of Alesia finally forced his surrender. Despite scattered outbreaks of warfare the following year, Gaul was effectively conquered. Plutarch claimed that during the Gallic Wars the army had fought against three million men (of whom one million died, and another million were enslaved), subjugated 300 tribes, and destroyed 800 cities.