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.
Tetricus I
During Tetricus' reign, the main threats to the Gallic Empire came from the Roman Empire and Germanic tribes. Tetricus also had to contend with dissent within the army and government. Tetricus was recognized as emperor by all of Gaul — except Gallia Narbonensis, which had been partially reconquered by the Placidianus, a general under Roman emperor Claudius Gothicus — and Brittania. He was not recognized by the province of Hispania, including Hispania Baetica, Lusitania and Hispania Tarraconensis, — which had earlier refused to recognize Victorinus as emperor — along with the city of Argentoratum (modern-day Strasbourg) in Germania; the provinces which did not recognize Tetricus chose instead to recognize Roman Emperor Aurelian, who had been proclaimed emperor in September 270 at Sirmium in Pannonia. By the time of Tetricus' rule, the Germanic tribes had become increasingly aggressive, launching raids across the Rhine and along the coast. Tetricus moved the capital of the Gallic Empire from Colonia to Augusta Treverorum in late 271, in order to guard against the Germanic tribes. Tetricus attacked them with some success, mainly during the early part of his reign, even celebrating a triumph for one of his victories. Later in his reign he was forced to withdraw troops and abandon forts, which allowed the border territories to be pillaged. Later Germanic raids were met with almost no opposition — one penetrated so far into Gallic territory that it reached the Loire. While Aurelian was concentrated upon attacking the Palmyrene Empire, which had broken away from the Roman Empire in 270, under Empress Zenobia, Tetricus was able to recover Gallia Narbonensis and south-eastern parts of Gallia Aquitania. During 273–274, Faustinus, provincial governor of Gallia Belgica, rebelled against Tetricus, however his revolt was swiftly crushed. Around this time, Tetricus also held the "quinquennalia", public games that took place every four years.