Still on guard
Fort Warren is a pentagonal bastion fort, made with granite, and built from 1833–1861. It was an important part of the defenses of Boston Harbor from 1861 through World War II, and during the Civil War was a prison for Confederate officers and government officials. It was decommissioned in 1947, and is now a tourist site. It was designated a National Historic Landmark in 1970 as a masterpiece of pre-Civil War coastal engineering, and for its role in the Civil War.