The unfinished Fort Jefferson proudly shows its power as covers an area of 16 acres of land in the Florida Keys Dry Tortugas National Park. Constructed from more than 16 million bricks, the coastal fortress is the largest brick masonry structure, and one of the largest forts, in the United States.
In December 1846, around five years after the Adams–Onís Treaty, in which the U.S. bought Florida from Spain for $5 million, Captain David Porter of the United States Navy was tasked with inspecting the Dry Tortugas island group to find the perfect location for a naval station to be erected in order to stop the pirates that were raging about the Caribbean Sea
Capt. Porter informed the United States Secretary of the Navy that the Dry Tortugas were no place for a fort, for there was no fresh water on the islands, plus there was little land on top of which a fort could stand. The island group was, however, considered a good location to site a lighthouse
An island by the name of Bush Key was chosen and construction began in 1825. One year later, there stood a 65.6 feet tall lighthouse made of brick, as well as a small house for the keeper. The island was later renamed Garden Key and the lighthouse Garden Key Light
A few years later, in 1829, the USS Florida under the command of Lieutenant Josiah Tattnall (later Commodore Tattnall) was also commissioned to survey the Florida Keys islands. His opinion of the Dry Tortugas was quite different to that of Captain Porter; Lt. Tattnall was rather pleased with what he encountered there. He reported that there were 11 keys with banks and reefs that afforded good protection, and even a natural inner and outer harbor of good depth. He further stated that it would be devastating if this place fell into the wrong hands
It was decided that a fort should be built there after all and in 1846 the construction of Fort Jefferson began, following the designs of Lt. Montgomery C. Meigs. The hexagonal fort has two defensive curtain walls that were 325 feet long and four that were 477 feet. There are bastions on each corner, covering every angle of the fort, each containing gun-rooms and magazines for gunpowder as well as a staircase made of granite. Each of the casemates had 150 guns, plus there were an additional 150 on the roof of the fort