Castle Pinckney.The gun overlooking the parapet of Castle Pinckney is a 15-inch Columbiad which used a powder charge of 40 pounds. The projectile weighed 428 pounds. A large number of these projectiles are stacked in the foreground. With an elevation of twenty degrees, the maximum range of this gun was 3,787 yards, or a little over two miles. This Fort was used as a prison for Union captives in 1861. In Battery Rodgers, within the corporate limits but nearly half a mile below the wharves and populous portion of the city of Alexandria, there were two magazines, one twelve by thirty feet and the other twelve by eighteen feet interior dimensions. These were sunk entirely below the terre plein, and protected by a cover of earth seventeen and a half feet thick, armed with five 200-pounders.