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.
Arverni
The Arverni later played an important role in the Gallic Wars of Julius Caesar from 58 BC to 51 BC. At first the Arvenian nobles tried to avoid confronting Caesar during his early incursions. They executed the leader Celtillus, evidently for trying to gain sovereignty over all the Gauls. In 52 BC, Celtillus' son Vercingetorix rallied his supporters to fight the Romans, but was expelled from Gergovia by the nobles, including his uncle Gobanitio. He then raised a great army in the country, and returned to the city where he ejected his opponents and was declared king. This accomplished, Vercingetorix forged an alliance with at least 15 Gallic tribes, requesting the presence of sons of chiefs to prove their alliance. He then led the majority of the Gauls and won the Gergovia battle against Julius Caesar and his cavalry did marvels in pursuing the Roman troops.
After Julius Caesar saved half of his legions and received food from other Gauls, he went further north to fight weaker opposition. Vercingetorix was defeated by Caesar at the Battle of Alesia, after several months where the legions built 14 ranges of military equipment around the city to lay siege upon the Gallic soldiers. After several weeks of support from the western Gallic people with large numbers of troops coming to support Vercingetorix from outside the city, the Gauls were close to merging the inner and outer forces on 2 occasions. When the outer forces decided to depart, Vercingetorix took the decision to surrender himself to the Romans in order to save the people of Alesia.