The West Demi-Bastion is the part of the southwestern wall that projects into the dry ditch. The southern half of the fort is built in the Vauban architectural style, an 18th century system based around the creation of a crossfire using bastions and demi-bastions. 19th century advances in artillery rendered this style obsolete, so the northern half of the fort is built in a cheaper and more efficient Prussian system called the "Polygonal Trace" which concentrates the firepower of the Fort in the direction of an anticipated attack.
The arch structures built into the wall are known as "casemates." When hit by a projectile, the bricks of the archways would compact together rather than collapsing in on themselves. Above the archway is a layer of rubble masonry, then a layer of flagging stone, then three feet of refuse stone and gravel. These layers would deaden the shock if a projectile were to strike the ramparts.