The Gauls are a barbarian people playable in Rome Total War. They are a Celtic people who were especially revered by the Romans because they managed to sack Rome.
The Gauls in real world were a group of tribes with Celtic roots. They were powerful warriors who wielded iron weapons. They did not live in a united state, like the Romans, but in a tribal structure. They usually fought amongst each other. Because of their own wars Caesar was able to conquer half Gaul before the Gauls realised they needed to unite. Caesar states in his De Bello Gallico that the druids use the Greek alfabet, but not to record history or religion. Because of this we only have records of the Roman side of the conflicts.