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.
Tetricus I
The Gallic Empire is the historiographic name given to a state composed of the Roman provinces which made up Britannia, Hispania, and Gaul, which broke away from the Roman Empire during the reign of Emperor Gallienus. Gallienus had become emperor after his father, Emperor Valerian, was captured by the Sassanids in 260; his rule was part of the Crisis of the Third Century (235–284), a period of intense political and military power struggles. Gallienus was overwhelmed by numerous issues, including several usurpers, and barbarian attacks in the Balkans and along the Rhine — one attack by the Franks pushed as far as Tarraco (modern-day Tarragona) in Hispania. Because Gallienus was unable to prevent the raids, Postumus, a military commander on the Rhine frontier, rose up and declared himself emperor; at about the same time he assassinated Saloninus, Gallenius' son and co-emperor, in Colonia (modern-day Cologne). Postumus focused on defending the Gallic Empire, and, in the words of ancient Roman historian Eutropius:
Gallienus attempted to invade the Gallic Empire twice, but was repulsed both times, forcing him to acquiesce in the secession. Although he was unable to conquer the Gallic Empire, Gallienus did ensure that the Roman Empire was defended; posting Aureolus, a military commander, in northern Italy, to prevent Postumus from crossing the Alps. Postumus was killed by his own soldiers in 269 in Mogontiacum (modern-day Mainz) while putting down a revolt by the usurper Laelianus, because he refused to allow them to sack the city. After the army killed Postumus, they elected Marcus Aurelius Marius, an officer, as Gallic Emperor. While some ancient sources hold that Marius reigned for only two days before being killed by Victorinus, who had served as "praetorian prefect" (commander of the praetorian guard) under Postumus, the quantity of coins issued by Marius indicate that he must have served for a longer time, a period of roughly three months. Victorinus declared himself emperor in mid-269 in Augusta Treverorum (modern-day Trier), two days after killing Marius. Victorinus' rule was recognized by the provinces of Britannia and Gaul, but not by those of Hispania.