Modernized and reinforced by Vauban at the end of the 17th century, the citadel of Sisteron has conserved its keep and its rampart walk from the 12th century as well as its ramparts from the 14th century. The underground staircase carved into the rock to connect the citadel to the city dates from the middle of the 19th century. Also marked with the imprint of Jean Errard, the military engineer of King Henry IV, the citadel of Sisteron constitutes a collection of works from diverse periods that mixes more than eight centuries of architecture.