The Tenth played a crucial part in the Gallic Wars, fighting under Caesar in virtually every battle.

At the beginning of the Gallic campaign, Caesar brought the 10th legion from Spain (with the 7th, 8th, and 9th legions). Almost immediately, in the summer of 58 BC, the legion fought in two major actions, the battles of Arar and Bibracte. They played a central part in Caesar’s defeat of the Helvetii tribes, preventing their migration from present-day Switzerland to western France.

Following the defeat of the Helvetii, the leaders of the Gallic tribes petitioned Caesar for his aid against Ariovistus, king of the German Suebi tribe. Prior to the battle, Ariovistus suggested a peace conference but insisted that each side should only be accompanied by mounted troops. Ariovistus made this a condition knowing that Caesar’s cavalry was composed mainly of Aedian horsemen whose loyalty to Caesar was questionable. Caesar ordered a group of his Gallic auxiliaries to dismount and had legionaries from the 10th ride in their place to accompany him to the peace conference. This incident earned the legion its nickname Equestris (mounted). One of the legionaries jokingly said that Caesar was better than his word: he had promised to make them foot guards, but now they appeared as equestrians.

Legio X saved the day in the Battle against the Nervians in 57 BC. Together with the IXth, the Xth defeated the Atrebates, moved against the Belgae on the other side of the river, and captured the camp. From that position, the Tenth could see how desperate the situation was for the XII Victrix and the VII, so it quickly charged downhill, crossed the river, and attacked the Nervii from the rear, trapping them/

In 55 BC Legio X was one of the two legions (together with the VII) which took part in Caesar’s first invasion of Britain. It is probable that it also participated in the second invasion in 54 BC.