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.
Gaul
The Roman proconsul and general Julius Caesar pushed his army into Gaul in 58 BC, on the pretext of assisting Rome's Gaullish allies against the migrating Helvetii. With the help of various Gallic clans (e.g. the Aedui) he managed to conquer nearly all of Gaul. While their military was just as strong 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. Julius Caesar was checked by Vercingetorix at a siege of Gergovia, a fortified town in the center of Gaul. Caesar's alliances with many Gallic clans broke. Even the Aedui, their most faithful supporters, threw in their lot with the Arverni, but the ever-loyal Remi (best known for its cavalry) and Lingones sent troops to support Caesar. The Germani of the Ubii also sent cavalry, which Caesar equipped with Remi horses. Caesar captured Vercingetorix in the Battle of Alesia, which ended the majority of Gallic resistance to Rome.