The difficulty of building on sand provided a challenge for the military engineers who were attempting to build Fort Pickens. One feature designed to prevent it from sinking into the sand was the use of a reverse arch as the foundation for the walls of the casemates. This view shows a reverse arch, which has been excavated to illustrate this structure.

The difficulty of building on sand provided a challenge for the military engineers who were attempting to build Fort Pickens. One feature designed to prevent it from sinking into the sand was the use of a reverse arch as the foundation for the walls of the casemates. This view shows a reverse arch, which has been excavated to illustrate this structure.