Deserted Places: Fort Jefferson: An abandoned island fortress off Florida

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In the lower Florida Keys, within the Dry Tortugas National Park there's an unfinished and abandoned island fortress, which is the largest masonry structure in the Americas. Fort Jefferson was built by the U.S. Army in 1846 to assist in the fight against piracy in the Caribbean Sea.

The design called for a four-tiered six-sided 1000 heavy-gun fort, with two sides measuring 415 feet (126 meters), and four sides measuring 564 feet (172 meters). On the parade ground inside the fort's massive brick walls there were living quarters for soldiers and officers, gunpowder magazines, storehouses, and other buildings required to maintain the fort. An important part of the construction was carried out by slaves.

Fort Jefferson's peak military population was 1,729. To support such a large population in an area lacking fresh water (hence the name 'Dry Tortugas'), an innovative system of cisterns was built into the walls of the fort. However, the system was never used in practice, cracks were created in the cisterns due to the enormous weight of the outer walls, allowing seawater to contaminate the fresh water supply.

During the Civil War, with construction still under way, Fort Jefferson was used as a prison for deserters. In 1867, a Yellow Fever epidemic killed many prisoners. By 1888 the Army turned the fort over to the Marine Hospital Service to be operated as a quarantine station as the cost of maintaining it due to the effects of frequent hurricanes and tropical climate could no longer be justified.

On January 4, 1935, President Franklin D. Roosevelt, who visited the area by ship, designated the area as a National Monument, while in 1992 the Dry Tortugas, including Fort Jefferson, was established as a National Park. Today, tourists can reach the island by ferry or by chartered seaplanes and private yachts and tour the abandoned Fort Jefferson.