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.
Gallic Wars
Caesar was across the Alps in Italy when he received the news. With only a single legion in Transalpine Gaul, the endangered province, he immediately hurried to Geneva and ordered a levy of several auxiliary units and the destruction of the Rhone bridge. The Helvetii sent an embassy to negotiate a peaceful passage, promising to do no harm. Caesar stalled the negotiations for fifteen days, and used the time to fortify his position with a rampart nineteen miles long and a parallel trench (De Bello Gallico, I, 7 and 8).
When the embassy returned, Caesar refused their request and warned them that any forceful attempt to cross the river would be opposed. Several attempts were quickly beaten off. The Helvetii turned back and entered negotiations with the Sequani, and with Dumnorix of the Aeduans, for an alternate route.(De Bello Gallico, I, 8 and 9).