redoubt -
(military) a temporary or supplementary fortification; typically square or polygonal without flanking defenses
fortification,
munition the addition of an ingredient for the purpose of enrichment (as the addition of alcohol to wine or the addition of vitamins to food)
A redoubt is a fort or fort system usually consisting of an enclosed defensive emplacement outside a larger fort, usually relying on earthworks, though others 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. 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.
