A redoubt is a fort or fort system usually consisting of an enclosed defensive emplacement outside a larger fort, usually relying on earthworks, although some are constructed of stone or brick. It is meant to protect soldiers outside the main defensive line and can be a permanent structure or a hastily constructed temporary fortification. The word means "a place of retreat". Redoubts were a component of the military strategies of most European empires during the colonial era, especially in the outer works of Vauban-style fortresses made popular during the 17th century, although the concept of redoubts has existed since medieval times. A redoubt differs from a redan in that the redan is open in the rear, whereas the redoubt was considered an enclosed work.