Probably outnumbering the lighthouse devotees reading these captions are powder magazine devotees, and I would have to throw in my lot with that latter group. Fort Jefferson's original detatched magazine was built at the southern extent of the parade ground, and there were a total of 32 magazines built into the fort's walls...but this monster came about later in the fort's life, when it was assumed that Fort Jefferson would be the depository for the US Navy's powder in these waters. The sign Keeping Powder Dry and Safe stands helpfully next to this magazine.