The current citadel of Sisteron results from successive consolidations, alterations, and modernizations. In the 16th century, following the damage from the French Wars of Religion, the crowning line of its upper rampart was reinforced to the north and south by a layering of bastioned structures. The south face was fitted out with four enclosures closed with doors, some of which defended by drawbridges. The north face had only three, significantly altered in the 19th century. Of Vauban's ambitious project of 1692, only the powder magazine and a well were built due to lack of resources. His recommendations, however, were followed during the work from 1842 to 1860: the curtain walls were raised, two cart gates were opened, casemates protected by escarps were built, and a cistern was fitted out to collect rainwater. Finally, the underground staircase connecting the fortress to the northern gate of Sisteron was dug.