The Fort, which stretches from the peak rocky outcrop called "Robine", is long and narrow. This form is quite unusual for a defensive work but had to take into account the terrain and the desire to include the 'Great' Tour "of the Middle Ages to work while protecting the city located at the foot of the hill. We are far here from the regular path of lowland forts.
You can enjoy this arcade in the small width of the Fort (25 meters wide and 200 meters long). The enemy projectiles fired on one of its sides might reach in the back the soldiers defending the opposite side. To remedy this problem that was created in the center of the structure, a longitudinal wall, called "scroll wall."
The platform is located to the right of access covers the underground stronghold added under Louis Philippe. It forms a step in the long, straight wall of southwest and thus addressed, there, the narrowness of the Fort.