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.
Gauls
Gaulish or Gallic is the name given to the Celtic language that was spoken in Gaul before the Latin of the late Roman Empire became dominant in Roman Gaul. According to Julius Caesar in his "Commentaries on the Gallic War", it was one of three languages in Gaul, the others being Aquitanian and Belgic. In Gallia Transalpina, a Roman province by the time of Caesar, Latin was the language spoken since at least the previous century. Gaulish is paraphyletically grouped with Celtiberian, Lepontic, and Galatian as Continental Celtic. The Lepontic language and the Galatian language are sometimes considered to be dialects of Gaulish.