The Saline Royale (Royal Saltworks) is a historical complex at Arc-et-Senans in the department of Doubs commissioned during the reign of Louis XVI (1774-92) and designed by Claude-Nicolas Ledoux.

The complex is listed as the World Heritage Site since 1982. It is notable for being the first major industrial architecture achievement implementing the Enlightenment ideals by improving architectural quality to match those of palaces or religious buildings.

For salt production the Saline Royale used firewood from nearby Forest of Chaux to boil the brine. It was also connected with saltworks of Salins-les-Bains (added in an extension to World Heritage Site in 2009) by a 21 km pipeline carrying the brine. The city was never started, however. All that was completed was the diameter and a semicircle of buildings of the saltworks.

In the second design, the entrance building sits at the midpoint of the semicircle and contains on one side guardrooms and on the other a prison and a forge. Other buildings on the semicircle include on the left, as one faces the entrance, quarters for carpenters and laborers, and on the right, marshals and coopers. At the center of the circle is the house of the Director, which has a belvedere on top. A monumental staircase led to a chapel that was destroyed by fire in 1918, following a lightning strike. On either side of the Director's house are the saltworks themselves. These two buildings are 80 meters long, 28 meters wide, and 20 meters high. They contain the drying ovens, the heating pots, the "Sales des Bosses", and the salt stores. At each intersection of the diameter and the semicircle sit buildings that housed the works' clerks. Behind the Director's house there is an elegant, small stables for the Director's horses.

The support of salt works by a state monopoly probably explains why this building is so grand. The gabelle was very unpopular and was one of the complaints that led to the French Revolution. The Revolution itself probably curtailed the building of the ideal city.

Since the end of salt production

The salt works produced 40,000 quintals of salt per year at its peak, all of which was exported to Switzerland. All production ceased in 1895 following a lawsuit that the inhabitants of Arc-and-Senans initiated, protesting the pollution of nearby wells. At the same time, the salt works was having difficulty in the face of competition from sea salt brought by rail.

thumb|Jeter des Fleurs sur l'Avenir, by the French painter [[Arnaud Courlet de Vregille, exposed in Royal Saltworks in 2006 for the Claude-Nicolas Ledoux's bicentenary]]

As mentioned above, a lightning bolt in 1918 destroyed the chapel. In April 1926, some of the buildings were dynamited, and many of the trees on the site were cut down. Still, on November 30, 1926, after a review that began in 1923, the Commission for Monuments declared the central pavilion and the entryway historical monuments. The Society for the Eastern Saltworks, still the owner of the Arc-et-Senans site, was not pleased with the decision. On 10 June 1927 the department of Doubs acquired the salt works and commenced restoration work in 1930.

During 1938, the site housed a camp for Spanish Republican refugees. Then, during October 1939, at the outbreak of World War II, the French military installed an anti-aircraft battery in the courtyard area. Also, a unit of engineers occupied some of the buildings. Still, February 20, 1940, saw the publication of the official announcement of the classification of the salt works and its surrounding wall as historical monuments.

In June 1940, German troops took up residence. From May 1941 to September 1943, the French authorities established an internment camp to hold the area's gypsies and others with no fixed address (Centre de Rassemblement des tziganes et nomades).

After the war, there was an extensive public campaign by artists, journalists and writers from the region to encourage the authorities to protect the site.

The Saltworks were a primary location in the 1961 film directed by Pierre Kast The Season for Love, part of the French New Wave.

In 1965, Marcel Bluwal used the director's house for the tomb of the Commander in his television adaptation of Molière's Dom Juan.

Since 1973, the royal salt works and the Institut Claude-Nicolas Ledoux have been members of the European network of cultural sites. Then in 1982, UNESCO listed the salt works as a World Heritage Site.