The Royal Saltworks of Arc-et-Senans, near Besançon France, was built by Claude Nicolas Ledoux. Its construction, begun in 1775 during the reign of Louis XVI, was a primary achievement of industrial architecture, reflecting progress of the Enlightenment. The large, semicircular complex was designed to have been followed by the building of an ideal city, a project that was never realized. The Great Saltworks of Salins-les-Bains was active for at least 1200 years until stopping activity in 1962. From 1780 to 1895, its salt water traveled through miles of wood pipes to the Royal Saltworks of Arc-et-Senans. It was built near the immense Chaux Forest to ensure its supply of wood for fuel. The Saltworks of Salins shelters an underground gallery from the 13th century including a hydraulic pump from the 1800’s that still functions.