Vocontii

The Vocontii were a Gallic people who lived on the east bank of the Rhône.

Their main towns were Lucus Augusti (modern Luc-en-Diois) and Vasio (modern Vaison-la-Romaine), but they occupied an extensive territory stretching from Vercors in the north, the buttresses of Mont Ventoux in the south-west, Manosque in the south-east and Embrun in the east. Their territory was therefore distributed over five current départements of France (Drôme, Isère, Hautes-Alpes, Alpes de Haute-Provence, Vaucluse).

During the 4th century BCE, the Celtic Vocontii became settled there, with an oppidum south of modern Vaison (Garcia p. 168); this seems to have been used to control trade between the Rhône and Durance rivers (Meffre).

The earliest historical mention of the Vocontii is from 218 BCE, the crossing of the Alps by Hannibal, as recounted in Livy (Ab Urbe Condita, 21.31):

The Vocontii became Romanized between 125 and 118 BCE, at the time of the conquest of the province of Gallia Narbonensis. During the 1st century BCE, the Vocontii signed a treaty of friendship (foedus) with Rome; this enabled them to keep a certain autonomy and their traditional institutions (Peck). One thus finds a praetor and a senate leading the city of Vaison, assisted by praefecti sent to the surrounding districts (pagi), which are advised by local assemblies (vigintiviri). Public municipal officials and slaves supplement this administrative flow chart.

...
Wikipedia