The Ravelin was designed to be a self-supporting fortlet in and of itself! Near the end of the US Civil War, Fort McHenry's Ravelin was mounted with those big Rodman Guns, and the inside was hollowed out and massively reinforced to serve as a powder magazine. Two rooms were built to hold powder and shot, and great efforts were made (in the form of angled stairways) to prevent secondary explosions that might result from an enemy's projectiles sneaking into the Ravelin. Look at all that gorgeous brickwork!!