It is sufficient to bend over the openings north (to the left when entering) to find that the rocky spur called "La Robine" extends and rises well above the Fort. Despite its length, it does not reach the summit of the mound. It is understandable that Vauban, who visited it in 1700, found it "bad" and was thinking of improving it. You can discover this project on the plan hanging on the wall.
Vauban foresees the addition of two bastions, one at mid-slope, the other at the top of the Robine. The financial difficulties of the kingdom delayed the execution of the works, and the Peace of Utrecht, signed in 1713, repelled the frontier with the Duchy of Savoy beyond the valley of the Ubaye. The Seyne fortress thus loses its strategic interest and the modifications envisaged are never realized. In fact, the Fort never experienced the "baptism of fire".
He was, however, occupied twice by the Austrians during the Austrian Succession War (1747/48) and after the fall of the Empire (1815). The Fort also serves as a prison. Piedmontese soldiers (1745), bishop Bonneval (1791), Austrian soldiers (1795) and Bas-Alpins who did not accept the coup d'état of Napoleon III (1851) were in turn locked up.