The major works of the citadel of Sisteron really began with the accession of King Henry IV in 1589. They followed the French Wars of Religion that ravaged Provence during the second half of the 16th century and during which the citadel served as a refuge for the Protestants and was besieged twice by the Catholics. The general plan for the citadel was established in 1611. Vauban's unaccomplished great project of 1692 arose from the invasion of the Haute-Durance by the Duke of Savoy, Victor Amadeus II. It inspired the redesigns carried out in the middle of the 19th century.