A masterpiece of Claude Nicolas Ledoux, the visionary architect of the Age of Enlightenment, the Saline royale of Arc-et-Senans is a rare testimony of the history of industrial architecture. Built between 1775 and 1779 to produce salt, it was organized as an integrated factory where almost the entire working community lived. Built in the shape of an arc of a circle, it housed both production and living quarters, with 11 buildings in all.