Claude Nicolas Ledoux created the Royal Saltworks of Arc-et-Senans, near Besançon. Its construction, begun in 1775 during the reign of Louis XVI, is the first important achievement of industrial architecture, reflecting the ideal of progress of the Enlightenment. This vast, semi-circular edifice was conceived to permit a rational and hierarchical organisation of work and should have been followed by the building of an ideal city, which was never realized.