A Civil War-era fort is situated on this 39-acre Harbor Island. The island was used for agricultural purposes for over 200 years until 1825, when it was claimed by the U.S. government for coastal defense. The fort was built between 1833 and 1861, being completed shortly after the beginning of the Civil War. Fort Warren was used as a training ground, patrol point, and a Civil War prison, which was favorably known for the humane treatment of Confederate prisoners. In the late 1890s the fort was modified to accommodate rifled ordnance being developed for coastal defense. It remained in use until 1947, when it was decommissioned. It was acquired by the Metropolitan District Commission for recreation and historic preservation in 1958 and was reopened in 1961 after an initial restoration.
Located seven miles from downtown Boston, Fort Warren is accessible by public ferry or private boat. The star-shaped fort features granite archways and stairways that open up to the fort roof, which provides panoramic views of the Boston skyline and Massachusetts Bay. Georges Island also contains overlooks and beaches, making it a destination for picnics and swimming. The island and fort are maintained and administered by the Massachusetts Department of Conservation and Recreation (DCR). Fort Warren was listed in the National Register of Historic Places and designated a National Historic Landmark District in 1970. Georges Island, inclusive of Fort Warren, became a centerpiece of the Boston Harbor Islands National Recreation Area upon the latter’s designation as a National Park unit in 1996.