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.
Gaul
The Roman proconsul and general Julius Caesar pushed his army into Gaul in 58 BC, on the pretext of assisting Rome's Gaullish allies against the migrating Helvetii. With the help of various Gallic clans (e.g. the Aedui) he managed to conquer nearly all of Gaul. While their military was just as strong 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. Julius Caesar was checked by Vercingetorix at a siege of Gergovia, a fortified town in the center of Gaul. Caesar's alliances with many Gallic clans broke. Even the Aedui, their most faithful supporters, threw in their lot with the Arverni, but the ever-loyal Remi (best known for its cavalry) and Lingones sent troops to support Caesar. The Germani of the Ubii also sent cavalry, which Caesar equipped with Remi horses. Caesar captured Vercingetorix in the Battle of Alesia, which ended the majority of Gallic resistance to Rome.