A World Heritage Site by UNESCO since 1982, the Saline Royale d'Arc et Senans (Royal Saltworks of Arc and Senans) is the masterpiece of Claude-Nicolas Ledoux, the visionary architect of the Enlightenment. It also bears a rare witness to the history of industrial architecture. The Royal Saltworks was established as a factory for the production of salt, by the will of Louis XV and built between 1775 and 1779, 10 years before the French Revolution.

At that time, salt was used mainly for food conservation, the manufacture of glass and silverware, agriculture and medicine. The state levied on its sale a heavy unpopular tax, the salt tax, which supplied much of the state coffers. The economic importance of salt was vital. The Royal Saltworks functioned as an integrated plant where lived most of the work community. Built in the shape of an arc, it housed living quarters and production facilities, 11 buildings in all: the director's house, stables, salt and office buildings, cooperage, building guards, blacksmithing.

The Salt ProductionThe salt production process was particularly complicated if one takes into account that the raw material was located about twenty kilometers from Arc-et-Senans. On the principle that it was easier "to have the water travel than the forest", wooden underground pipes were used to bring in brine (salt water) from the point of extraction, Salins. As for the fire wood needed to extract the salt, the nearny forest of Chaux, the largest in France at the time, was exploited. Once delivered on site, the brine was heated in large pans to carry out the evaporation of water. The salt was then sold in grain or molded bricks according to its destination.

The Saline Royale was closed in 1895 as it was rendered obsolete by the emergence of new technologies. Abandoned, looted, damaged by fire in 1918, it was used like a quarry, its stones were traded, when in 1927 the Department of Doubs acquired it, saving it from ruin. Three successive campaigns of restoration lasting 60 years and which were completed in 1996 gave it a new life. The architecture of the Saline Royale, its history and its restoration make it a very unique monument.

The Architectural Project Claude-Nicolas Ledoux conceived his project as a complete package. It includes eleven buildings, five workshops and housing workers' homes, arranged in a huge semicircle, centered around the House of the Director. It is a stunning example of enlightenment architecture applied to a monument to industrial use. Much later, when Ledoux was imprisoned during the Revolution, he imagined, to expand the Saline into the "cite ideale de Chaux", but this remained a project. The buildings arranged in a semicircle are at the heart of Ledoux's idea to create a perfect structure for a new industrial and social era. The harmony of the surroundings and the symbolic found in the composition of the ensemble was aimed to shape a society that elevates the soul of its people, creating virtue and collective happiness, while maintaining work as the ultimate value at the centre.