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.
Gallic Empire
It was established by Postumus in 260 in the wake of barbarian invasions and instability in Rome, and at its height included the territories of Germania, Gaul, Britannia, and (for a time) Hispania. After Postumus' assassination in 268 it lost much of its territory, but continued under a number of emperors and usurpers. It was retaken by Roman emperor Aurelian after the Battle of Châlons in 274.