Marseille or Marseilles is the prefecture of the French department of Bouches-du-Rhône and of the Provence-Alpes-Côte d'Azur region. S…Marseille or Marseilles is the prefecture of the French department of Bouches-du-Rhône and of the Provence-Alpes-Côte d'Azur region. Situated in the Provence region of southern France, it is located on the coast of the Gulf of Lion, part of the Mediterranean Sea, near the mouth of the Rhône river. A resident of Marseille is a Marseillais.