The Fort de Joux or Château de Joux is a castle, transformed into a fort, located in La Cluse-et-Mijoux, in the Doubs département, in the Jura mountains of France. It commands the mountain pass "Cluse de Pontarlier". During its long history, Fort de Joux has gone through successive transformations. The first structure, in the 11th century, was made of wood. In the next century the lords of Joux rebuilt it in stone. It passed, along with all of Franche-Comté, into the hands of Burgundy, and then the Hapsburgs and the Spanish. It was finally regained for France in 1687 by Louis XIV.