Fort Warren

Fort Warren occupies Georges Island, a 40-acre oval at the throat of Boston Harbor. Construction began in 1834 under Lt. Col. Sylvanus Thayer of the Corps of Engineers and was finished during the Civil War. It is a bastioned star fort built mostly of Quincy granite, with walls eight feet thick enclosing a parade ground of about four acres. Casemate guns, howitzers and Columbiads once armed its fronts. Later modernization in 1871-1876 and 1898-1899 added gun mounts, and a power plant and a World War I mine storage building also survive, yet the star fort remains structurally close to its mid-19th-century form. The fort is valued as a leading example of the Third System of coastal defense and as Thayer's chief engineering work. It is also considered New England's most significant Civil War site because Confederate commissioners Mason and Slidell, generals, and Vice President Alexander Stephens were held there. The state now manages it as a park.