The Saline Royale (Royal Saltworks) is a historical building at Arc-et-Senans in the department of Doubs, Eastern France. It is next to the Forest of Chaux and 29.2 kilometres (18.1 miles) to the southwest of Besançon. The architect was Claude-Nicolas Ledoux (1736–1806), a prominent Parisian architect of the time. The work is an important example of an early Enlightenment project in which the architect based his design on a philosophy that favored arranging buildings according to a rational geometry and a hierarchical relation between the parts of the project.