Portsdown Hill is a long chalk ridge in Hampshire, England. The highest point of the hill lies within Fort Southwick at 131m above sea level. The ridge offers good views to the south over Portsmouth, the Solent, Hayling Island and Gosport, with the Isle of Wight beyond. The hill is on the mainland, just to the north of Ports Creek, which separates the mainland from Portsea Island, on which lies the main part of the city of Portsmouth, one of the United Kingdom's main naval bases. To the north lies the Forest of Bere, with the South Downs visible in the distance. Butser Hill can be seen on a clear day. The hill is formed from an inlier of chalk which has been brought to the surface by an east–west upfold of the local strata known as the Portsdown Anticline. Southwick House is close by the north side of the hill, the HQ for U.S. General Dwight D. Eisenhower during the D-Day invasions; the generals prayed together before D-Day at Christ Church Portsdown, on the hill, which has a memorial window. The A3(M) motorway cuts through the east side of the hill while the original A3 climbs over the centre by the George Inn pub and Christ Church. The nearest railway stations (from west to east) are Portchester, Cosham and Bedhampton. There are many stories about real and imagined tunnels in the hill. The area contains active military research establishments, including one of the core sites of Dstl (known as Dstl Portsdown West) and sites run by QinetiQ. Part of the hill has been designated a Site of Special Scientific Interest. Most of the southern flank of the ridge is designated as access land under the Countryside and Rights of Way Act 2000 and thereby freely available for the public to enjoy on foot. During the early part of the English Civil War Royalist forces from Portsmouth were involved in a number of skirmishes with Parliamentarians on the hill In the Victorian era the hill was home to a fair on Easter Mondays. Portsdown Forts The forts on Portsdown Hill were built as a result of the 1859 Royal Commission, as part of a series of fortifications built to defend Portsmouth and its dockyard (which is 8 kilometres away) from a possible attack from inland, as the development of rifled gun barrels made it possible for an invading army to