The Royal Saltworks of Arc-et-Senans was built during the reign of Louis XVI and is the modern and Utopian extension of the Great Saltworks of Salins-les-Bains. Built by Claude Nicolas Ledoux, it was the first major achievement of industrial architecture, reflecting the ideal of progress in the Age of Enlightenment. The vast, semicircular complex was designed to permit a rational and hierarchical organization of work and was to have been followed by the building of

an ideal city, whose unfinished Utopian architecture still carries the full impact of its futuristic message.

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The saltworks in Salins-les-Bains and Arc-et-Senans UNESCO world treasures and demonstrate an uninterrupted, chronological timeframe during which the extraction of salt continued in Salins, certainly from the Middle Ages, and probably from prehistoric times, through to the 20th century. Spa activity has extended its use to the present.