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.
Western Roman Empire
With the assassination of the Emperor Alexander Severus on 18 March 235, the Roman Empire sank into a 50-year period of civil war, now known as the Crisis of the Third Century. The rise of the bellicose Sasanian Empire in place of Parthia posed a major threat to Rome in the east, as demonstrated by Shapur I's capture of Emperor Valerian in 259. Valerian's eldest son and heir-apparent, Gallienus, succeeded him and took up the fight on the eastern frontier. Gallienus' son, Saloninus, and the Praetorian Prefect Silvanus were residing in Colonia Agrippina (modern Cologne) to solidify the loyalty of the local legions. Nevertheless, Marcus Cassianius Latinius Postumus – the local governor of the German provincesrebelled; his assault on Colonia Agrippina resulted in the deaths of Saloninus and the prefect. In the confusion that followed, an independent state known in modern historiography as the Gallic Empire emerged.