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.
Campaign history of the Roman military
During a term as praetor in Iberia, Pompey's contemporary Julius Caesar of the Roman Julii clan defeated the Calaici and Lusitani in battle. Following a consular term, he was then appointed to a five-year term as Proconsular Governor of Transalpine Gaul (current southern France) and Illyria (the coast of Dalmatia). Not content with an idle governorship, Caesar strove to find reason to invade Gaul, which would give him the dramatic military success he sought. To this end he stirred up popular nightmares of the first sack of Rome by the Gauls and the more recent spectre of the Cimbri and Teutones. When the Helvetii and Tigurini tribes began to migrate on a route that would take them near (not into) the Roman province of Transalpine Gaul, Caesar had the barely sufficient excuse he needed for his Gallic Wars, fought between 58 BC and 49 BC. After slaughtering the Helvetii tribe, Caesar prosecuted a "long, bitter and costly" campaign against other tribes across the breadth of Gaul, many of whom had fought alongside Rome against their common enemy the Helvetii, and annexed their territory to that of Rome. Although "fierce and able" the Gauls were handicapped by internal disunity and fell in a series of battles over the course of a decade.