Fort Warren is a historic fort on the 28-acre (110,000 m) Georges Island at the entrance to Boston Harbor. The fort is pentagonal star fort, made with stone and granite, and was constructed from 1833?1861, completed shortly after the beginning of the American Civil War. Fort Warren defended the harbor in Boston, Massachusetts, from 1861 through the end of WWII, and during the Civil War served as a prison for Confederate officers and government officials. The fort remained active through the Spanish?American War and World War I, and was re-activated during World War II. It was permanently decommissioned in 1947, and is now a tourist site. It was designated a National Historic Landmark in 1970 as a masterpiece of coastal engineering of the pre-Civil War period, and for its role in the Civil War. It was named for Revolutionary war hero Dr. Joseph Warren, who sent Paul Revere on his famous ride, and was later killed at the Battle of Bunker Hill.
-- From Wikipedia
Fort Warren was built from 1833 to 1861 and was completed shortly after the beginning of the American Civil War. The Army engineer in charge during the bulk of the fort's construction was Colonel Sylvanus Thayer best known for his tenure as Superintendent of the United States Military Academy at West Point, New York. During the Civil War, the island fort served as a prison for captured Confederate army and navy personnel, elected civil officials from the state of Maryland, as well as Northern political prisoners.
James M. Mason and John Slidell, the Confederate diplomats seized in the Trent affair, were among those held at the fort. Military officers held at Fort Warren include Richard S. Ewell, Isaac R. Trimble, John Gregg, Adam "Stovepipe" Johnson, Simon Bolivar Buckner, Sr., and Lloyd Tilghman. High ranking civilians held at Fort Warren include Confederate Vice President Alexander H. Stephens, and Confederate Postmaster General John Henninger Reagan. The prison camp had a reputation for humane treatment of its detainees. When the camp commander's son, Lieutenant Justin E. Dimick, left Fort Warren for active duty in the field with the Second U.S. Artillery, he was given a letter from Confederate officers in the camp urging good care should he be captured. (He was later mortally wounded at Chancellorsville in May, 1863.)
The famous Union marching song John Brown was written at the fort using a tune from an old Methodist camp song. The song was carried to the Army of the Potomac by the men of the "Webster Regiment" (12th Massachusetts Infantry) who had mustered in at Fort Warren. Julia Ward Howe heard this song while visiting Washington DC. At the suggestion of her minister, Howe was encouraged to write new words. The Battle Hymn of the Republic, which was initially published as a poem, was later matched with the melody of the "John Brown" song and became one of the best remembered songs of the Civil War era. (See also:List of Civil War POW Prisons and Camps)
-- From Wikipedia