Luc-en-Diois is a commune in the Drôme department in southeastern France. It is situated on the river Drôme. The Latin name of Luc-en-D…Luc-en-Diois is a commune in the Drôme department in southeastern France. It is situated on the river Drôme. The Latin name of Luc-en-Diois, Lucus Augusti or Lucus for short, evokes a crowned wood of the Gauls. Perhaps this is the origin of this Roman capital installed in the first century BC at the foot of the mountains of Diois. It shared with Vaison-la-Romaine the title of chief city of Vocontii, an important romanized Gallic people..