Celtic warfare
The "Gallic Wars" were a series of military campaigns waged by the Roman proconsul Julius Caesar against Gallic tribes, lasting from 58 BC to 51 BC. The Romans would also raid Britannia and Germania, but these expeditions never developed into full-scale invasions. The Gallic Wars 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. The wars paved the way for Caesar to become the sole ruler of the Roman Republic.
Postumus
Marcus Cassianius Latinius Postumus was a Roman commander of Batavian origin who ruled as emperor in the west. The Roman army in Gaul threw off its allegiance to Gallienus around the year 260, and Postumus assumed the title and powers of emperor in the provinces of Gaul, Germania, Britannia and Hispania, thereby founding what scholars have dubbed the Gallic Empire. He ruled for the better part of ten years before he was murdered by his own troops.