Why were palisades placed in ditches or behind glacis slopes?

In the context of military science, the use of palisades—rows of sharpened wooden stakes—served as a critical defensive refinement within the "sunken profile" of fortress design.12

When fortress walls were lowered into the ground to protect them from direct artillery fire, designers utilized ditches and glacis slopes to create a defensive barrier. Placing palisades in the ditch or immediately behind the glacis provided an additional physical obstacle for attackers attempting to breach the fortification. These stakes were intended to impede enemy movement and disrupt assaults, effectively complementing the defensive advantages provided by the sunken profile, which allowed defenders to remain concealed while maintaining clear fields of fire from the parapet.2

By integrating these obstacles, military engineers sought to maximize the defender's ability to utilize their weapons while forcing the enemy to navigate hazardous, exposed terrain.23