Castellane is a commune in the Alpes-de-Haute-Provence department in the Provence-Alpes-Côte d'Azur region in Southeastern France. Wit…Castellane is a commune in the Alpes-de-Haute-Provence department in the Provence-Alpes-Côte d'Azur region in Southeastern France. With a population of 1,470, it has the distinction of being France's least populated subprefecture, ahead of Largentière in Ardèche.