ntended for the production of salt, the factory was built between 1775 and1779 by Claude-Nicolas Ledoux, one of the greatest architects of the Age of Enlightenment. The Saltworks was constructed in the form of a semicircle and designed to include not only the production units but also workers’ living quarters. At the time, salt was of paramount economic importance. The raw material, that is to say the bittern or salt water, was extracted from the old salt mine of Salt water, was extracted from the old mine of Salins-Les-Bains. It was then carried the 23 km to Arc-et-Senans via underground wooden pipelines. Once at the saltworks, the salt water was heated by firewood brought in from the nearby Forest of Chaux. After the evaporation stage, the salt was sold in grain form or mixed into bread, depending on the destination. But the significance of the Saltworks stretches beyond its original system of operation and its exceptional architecture, for it was intended as a model for the expression of Ledoux’s philosophical thought- the “Ideal City of Chaux”. The Royal Saltworks rapidly became obsolete as a result of the technical advances up by the Doubs department in 1927, since when successive campaigns have restored the site to its former glory. 11 buildings designed in a semicircle around the Director’s Residence: workshops and the living quarters of the berniers (salt-workers) and their families, partially open to the public.