Farlington Redoubt was built on the site as a result of the 1859 Royal Commission, as part of a series of fortifications built to defend Portsmouth and its dockyard (which is 5 miles away) from a possible attack from inland, as the development of rifled gun barrels made it possible for an invading army to land elsewhere, circle around to the top of the hill and bombard the city from there, rendering the existing Hilsea Lines at the bottom of the ridge useless.