Gauls
In 58 BC Julius Caesar launched the Gallic Wars and had conquered the whole of Gaul by 51 BC. He noted that the Gauls (Celtae) were one of the three primary peoples in the area, along with the Aquitanians and the Belgae. Caesar's motivation for the invasion seems to have been his need for gold to pay off his debts and for a successful military expedition to boost his political career. The people of Gaul could provide him with both. So much gold was looted from Gaul that after the war the price of gold fell by as much as 20%. While they were militarily just as brave as the Romans, the internal division between the Gallic tribes guaranteed an easy victory for Caesar, and Vercingetorix's attempt to unite the Gauls against Roman invasion came too late. After the annexation of Gaul a mixed Gallo-Roman culture began to emerge.
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.