Fort Warren is an impressive 19th century fort, covering much of George’s Island’s 28-acres. The fort is located in the centre of the main shipping channel for Boston Harbor, a position that made it ideal for harbour defence. Fort Warren is the second largest fort in New England (Fort Adams being the largest).
George’s Island was first fortified during the Revolution by the French, but the present Fort Warren was constructed between 1833-1860. It not only served as Boston's primary seacoast defence, but also was used a prison for Confederate soldiers during the Civil War. The fortifications were upgraded in the 1890s-1900s, with the post under military control through WWII.
Most of Fort Warren is a classic 19th century granite walled fort, using angular corner bastions to provide covering fields of fire. The stone fort was surrounded by angular earthworks or glacis, which helped defend against direct fire. One of the most unique features of the fort is the casemated demi-lune, or moon-shaped fort, located on the northern side of the island. I have never seen this defensive feature in North America, and suspect this to be a very unique feature.