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.
Roman–Gallic wars
223-193BC: After this came a concerted Roman policy aimed at conquering Gallic territories south of the Alps. Rome invaded the territory of the Insubres in 223BC, and took Clastidium, Acerrae and Mediolanum in 222BC. Rome fought Carthage in the Second Punic War (218-201BC), and the Gauls typically sided with Carthage. After the war, Rome took Bononia (196BC), Placentia (194 BC) and Mutina (193 BC). After this, many of the surviving Boii retreated north across the Alps to form a new state, Boihaemum.