Gallic Wars
The Gallic Wars were a series of military campaigns waged by the Roman proconsul Julius Caesar against several Gallic tribes. Rome's war against the Gallic tribes lasted from 58 BC to 50 BC and culminated in the decisive Battle of Alesia in 52 BC, in which a complete Roman victory resulted in the expansion of the Roman Republic over the whole of Gaul (mainly present-day France and Belgium). While militarily just as strong as the Romans, the internal division between the Gallic tribes helped ease victory for Caesar, and Vercingetorix's attempt to unite the Gauls against Roman invasion came too late. The wars paved the way for Julius Caesar to become the sole ruler of the Roman Republic.
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.