The urbanization of Gallic culture had probably far more to do with trade with the Greeks, whom not only used the Danube River as a highway into Celtic lands, but established colonies on the Mediterranean coast such as the future Marseille, Nice, Empuries, and Monaco. In other respects, the Celts were making their own achievements long before Rome achieved prominence in Italy. They were minting coins and building roads before the Romans did, and basic items of Roman wargear (chainmail, shortswords, pilum, and Montifortino-style helmets) are believed to have originated with them.
One notable Celtic power in Gaul, the Arverni, located in modern Auvergne, held considerable sway for over a century between 250-120 BCE. They controlled a number of goldmines in their territory, sat on the main trade routes from north to south, were major manufacturers of goods, and from their wealth, controlled a powerful and well-equipped professional army. They ruled Gaul as a military hegemony, not unlike how Rome came to rule Italy in the first place. This ended during the reign of one King Bitutius, whom was defeated by the Consul Fabius Maximus in 123 BCE.
Gaul, in the time of Caesar, was very different politically than a century before. Tribes, such as the Allobroges (Savoy, Vivarais, and Dauphine), and the Aedui (Saone-et-Loire, Cote-d'Or, and Nievre) were Roman allies for much of the Gallic Wars. The few professional companies among the native Gallic forces were either serving under Caesar as mercenaries, or were in the service of Rome's Gallic allies whom assisted Caesar. There was even one Legion raised by Caesar composed of Gallic provincials, called the Legio V Alaudae.