4. THE NORTH MAGAZINE. On the second day of the bombardment Federal projectiles, exploding near the entrance to this powder magazine, threatened to blow up the Confederates with their own powder. The interior walls of the magazine are from 12 to 15 feet thick. 5. THE NORTHWEST BASTION. A bastion is a part of a fort which extends out from the main wall, with embrasures and loopholes to permit lateral fire along the walls. Fort Pulaski had only demibastions, or half bastions, as they extend out only in one direction and give protection to only one wall. The rectangular openings through the outer walls of the fort are embrasures to permit the firing of cannon. The embrasures in the bastions are angled to bring a crossfire on the main drawbridge and on the point of the demilune. The slot under each embrasure was to receive the tongue of a gun carriage which was then held in place by a large iron pin dropped through the round hole in the floor of the embrasure. The openings in the ceiling above the embrasures are smoke vents. The circular grooves in the floor originally held iron tracks on which the wheels of the gun carriages turned. The slots and grilled trapdoors in the floors of the casemates are to provide ventilation under the floors. The round pegs in the floor cover iron spikes that hold the planks in place and originally served to reduce the hazard of a powder explosion when the guns were in use. Hobnails in soldiers’ boots on contact with exposed spikes might have resulted in a dangerous shower of sparks. 6. THE GUN GALLERIES. The casemated gun galleries, which surround the parade ground on four sides and give to Fort Pulaski the atmosphere of a cloistered monastery, contain fine examples of brick masonry. The arches were constructed over wooden forms, each brick being hand cut to fit its special place. The joints were mortared from above and, when the arches were firm and strong, the wooden forms were removed. 7. THE WATER SYSTEM. Under the brick pavements, which replace the wooden floors in the two center casemates of each gallery, are water cisterns. There are 10 of these cisterns, or storage tanks, in the fort, each capable of holding 20,000 gallons of water. During rainstorms, water falling on the top of the fort seeps through about 3 feet of earth and a foot of oyster shell until it reaches the lead-covered brick roof, whence it is diverted through pipes to the cisterns. Overflow water from the roof emerges through weep holes between the arches high on the walls facing the parade ground. 8. THE TERREPLEIN. The flat surface on top of the rampart of the fort is called the terreplein and contains brick and granite platforms for mounting guns. From this high level, guns had a range of fire greater than those mounted in the casemates below. The breast-high parapet on the outer edge of the terreplein was for the protection of both guns and gun crews. The recesses in the parapet wall were to allow gun carriages to swing freely.