Designed by Captain E. H. Steward of the Royal Engineers, the circular fort was first planned in 1859. It was built as a result of the
Royal Commission to guard the new
Portland harbour and
Royal Navy institutions on the island. Due to subsidence, the fort was constructed on a granite base, based on a diameter ring of stone laid down on the seabed. The main floor consists of gun rooms and ports for 14 heavy guns. Below the gun floor are the shell and cartridge stores and engine rooms. The fort also has its own harbour and ancillary barrack buildings. The fort cost £75,968 to build. In 1892, the fort was installed with seven 12.5-inch RML cannons, and these were replaced in 1907 by two 6-inch BL guns and two 12-pounder QF guns. During World War I, it was armed with two 6-inch BL Mk. VII guns. During World War II, the fort was used as an examination battery. In 1995, the Dorset Sculpture Trust attempted to gain a grant from the Millennium Fund to turn the site into an arts centre. ==References==