Fort Jefferson

Fort Jefferson stands on Garden Key in the Dry Tortugas, 68 miles west of Key West. It covers 16 acres and is built from more than 16 million bricks, which makes it the largest brick masonry structure in the Americas. Among American forts only Fort Monroe in Virginia and Fort Adams in Rhode Island are bigger. It was named for Thomas Jefferson.

The plan is a six-sided outline with two tiers of casemates, which are vaulted gunrooms opening toward the sea. Two walls measure 325 feet and four measure 477. The corners hold bastions with gunrooms, powder magazines and a granite spiral staircase. Each tier was meant for 150 guns, with another 150 on top, and the parade ground inside covered 13 acres with barracks, quarters and a hospital.

Fresh water was a problem on an island with none. Sand-filled columns in the walls were supposed to filter rainwater into underground cisterns, but the stored water was unfit for drinking and could be used only for washing and cooking. Only the runoff stored under the parade ground was drinkable, and during the Civil War two steam condensers distilled seawater. The Garden Key lighthouse was enclosed within the walls, and the current metal light tower was installed on top of a wall in 1876.

Work began in December 1846 and was about half complete in 1860. Most of the labor came from enslaved people hired out by their owners in Key West and elsewhere in Florida, with some Irish immigrants also employed. The use of enslaved labor ended in 1863. The seawall was finished in 1872 and the fort ended up with 243 large-caliber guns.

During the Civil War the Union kept the fort, and from 1861 it also held soldiers sentenced by courts-martial. Lincoln replaced execution with imprisonment here for deserters. In 1865 four civilians convicted in the Lincoln assassination conspiracy arrived. A yellow fever epidemic in 1867 killed many prisoners and the post surgeon. One of the four civilians, Samuel Mudd, helped treat the sick, and three of them were later pardoned.

Hurricanes and yellow fever convinced the War Department to pull the garrison in 1874. The fort served as a quarantine station from 1889, then as a naval coaling stop, and sat abandoned for long stretches. In 1908 the islands became a federal bird reservation. President Franklin D. Roosevelt made the fort a national monument in 1935 and the Works Progress Administration restored it until 1938. It joined the National Register of Historic Places in 1970, and in 1992 the Dry Tortugas became a national park.