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Fort Jefferson

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1846–1875, Joseph Totten. Garden Key.
  • (Courtesy of State Archives of Florida, Florida Memory)

Florida’s strategic location between the Gulf of Mexico and the Atlantic Ocean has left the state with a substantial heritage of significant military installations. One of the most remote is Fort Jefferson, a brick fortress built on a small key in the Dry Tortugas, 68 miles west of Key West. Fort Jefferson is the largest of a string of fortifications constructed to protect the Atlantic and Gulf coasts of the United States in the nineteenth century.

The location for Fort Jefferson was first scouted in 1824, three years after Spain ceded Florida to the United States. At the time, piracy constituted a serious problem in the Gulf and the Caribbean, and naval planners sought to build fortified ports as bases from which to patrol the area’s shipping routes. At first, Garden Key—the eventual site of Fort Jefferson—was dismissed as too small and too devoid of fresh water for military use. A lighthouse was built instead to mark the shallow reefs surrounding the keys in 1825. A second expedition to Garden Key in 1829 produced a much different appraisal of the site, and it was decided to build a large fortress with a substantial port. Fort Jefferson was designed to accommodate 1,500 men to operate 450 guns, and the harbor was large enough to allow numerous ships of the line to ride at anchor.

Construction began in 1846, and involved significant logistical challenges. Most building materials were brought by ship, including some 16 million bricks. Only the coral and sand used in the mortar could be sourced locally. The additional challenge of providing shelter, food, and water for construction workers on an island only slightly larger than the fort itself also proved difficult, and work would continue for 29 years, slowed by the Civil War and periodic outbreaks of yellow fever. Most of the unskilled laborers used to build the fortress were enslaved African Americans from St. Augustine and Key West; military prisoners took their place during the Civil War.

Fort Jefferson is hexagonal in plan, with 45-foot-tall battlements that extend for over half a mile in perimeter and are punctuated at the six corners by bastions. The battlements include a thick outer wall layer intended to resist bombardment backed by a three-level arcaded structure that accommodated large guns in open casemates on the lower two tiers. The massive structure was built of red clay brick supplied by Baker and Abercrombie of Pensacola. A 70-foot-wide moat and breakwater surround the fort in order to protect the structure from the erosive effects of waves.

The Dry Tortugas derive their name from the absence of drinkable ground water on the islands. The fortress incorporated an ingenious system for collecting, filtering, and storing rainwater for potable use by the garrison. Rainwater running off the battlements would pass through hollow brick columns containing sand (a natural filter) that surround the fort’s courtyard; the water then collected in underground cisterns. Unfortunately, the fort’s concrete foundations settled too much on the coral bedrock, leading to cracks in the cistern walls that allowed seawater to foul the drinking water. As a result, the system was never used.

As Chief Engineer of the U.S. Army, Colonel Joseph Gilbert Totten oversaw the construction of all American fortifications between 1838 and 1864, including Fort Jefferson and the contemporaneous Fort Zachary Taylor in Key West. An expert in masonry construction who had also written a treatise on mortar and cement, Totten was particularly skilled in the design of coastal fortifications. Fort Jefferson incorporated one of Totten’s best known inventions, the Totten shutter, which protected gunners from enemy fire by using steel doors in each embrasure. These doors were balanced to open and close automatically when the gun behind them fired. One shortcoming of the shutters was that when their wrought-iron anchors oxidized in the presence of salt water, the resulting expansion caused the masonry walls to partially collapse. The National Park Service restored the escarpment using salvaged bricks and installed replica Totten shutters between 2007 and 2010.

While the fortress is impressive in bearing, it had already become obsolete during its construction. Advances in naval warfare, such as the introduction of the rifled gun, made the structure outdated by the 1860s, and it was never completed. Fort Jefferson was used as a Union military prison during the Civil War, where it confined troops accused of desertion. Fort Jefferson’s most famous prisoner, Dr. Samuel Mudd, arrived in 1865 after he was convicted of treason for setting presidential assassin John Wilkes Booth’s broken leg. Mudd proved instrumental in saving many of the fort’s inhabitants during the yellow fever epidemic of 1867, and was pardoned for his efforts by President Andrew Johnson. The 1936 John Ford film The Prisoner of Shark Island, which dramatized the story of the physician whose infamous adherence to the Hippocratic Oath led to his incarceration, was largely set at Fort Jefferson (although it was filmed in Fox Studios in Los Angeles).

President Franklin Roosevelt declared Fort Jefferson a National Monument on January 4, 1935, and soon after Charles Peterson prepared the original Historic American Buildings Survey report on the site. In 1992, Fort Jefferson was included as part of the Dry Tortugas National Park.


Robinson, Willard. American Forts, Architectural Form and Function. Urbana: University of Illinois Press, 1977.

Works Progress Administration. “History of the Fort Jefferson National Monument. Part One: The Fort at Garden Key, 1846-1860.” Key West, Florida, 1936.

Writing Credits

David Rifkind
John Stuart
David Rifkind



  • 1846

    Design and construction


David Rifkind, "Fort Jefferson", [Key West, Florida], SAH Archipedia, eds. Gabrielle Esperdy and Karen Kingsley, Charlottesville: UVaP, 2012—,

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