They were designed by renowned military architect Sébastien Le Prestre de Vauban (1633–1707) during the reign of King Louis XIV.

After taking the advice of specialists, they decided to mount an application in the form of a network representing the entire genius of the architect Sébastien Le Prestre de Vauban, to best meet the criteria issued by UNESCO.

(In competition with the potential UNESCO World Heritage nomination, consisting of the works of Le Corbusier, each country could submit only one file each year).

The Citadel has been nicknamed La belle inutile (the beautiful useless one) by residents as it has never been directly involved in heavy fighting, and ultimately failed to prevent the Germans from occupying the city in either World War.

Outside, Le Mur des Fusillés (the wall of the people executed by a firing squad) pays tribute to the 218 members of the French Resistance shot in the citadel's ditch during World War II.

Mount Saint-Etienne occupies the neck of an oxbow formed by the river Doubs, giving the site a strategic importance that Julius Caesar recognised as early as 58 BC.

The Citadel is built on top of a large syncline on a rectangular field crossed across its width by three successive bastions (enclosures, or fronts) behind which extend three plazas.

It is an 18m-high polygonal defensive tower built from 1693 to 1695 using a plan by Vauban on the Sillon at Camaret-sur-Mer, as part of the fortifications of the goulet de Brest.

It has three levels and is flanked by walls, a guardhouse and a gun battery which can hold 11 cannons as well as a cannonball foundry added in the French Revolution period.

They were built in 1679 in order to facilitate trans-border crossings with Spain, and contain a square citadel and fortified town walls with 25 sentry posts.

[4] Two sites initially considered were removed from the final list: A château in Bazoches, Nièvre, and the citadel and walls surrounding Le Palais in Belle-Île-en-Mer, Morbihan.