Ardennes (ärdĕnˈ) [key], department (1990 pop. 295,700), NE France, in Champagne. The capital is Charleville-Mézières. Ardennes is also the name of a section of the eastern branch of an ancient mountain chain resulting from Hercynium folding between 345 million and 225 million years ago. The western edge of the chain is located in France, while the remainder extends into Belgium, Luxembourg, and Germany.