The South Downs are a range of chalk hills in the south-eastern coastal counties of England that extends for about 260 sq mi (670 km2)[1] across the south-eastern coastal counties of England from the Itchen valley of Hampshire in the west to Beachy Head, in the Eastbourne Downland Estate, East Sussex, in the east.

There is a rich heritage of historical features and archaeological remains, including defensive sites, burial mounds and field boundaries.

However, starting in 1940 with government measures during the Second World War to increase domestic food production – which continued into the 1950s - much grassland was ploughed up for arable farming, fundamentally changing the landscape and ecology, with the loss of much biodiversity.

[7] These hills are prefixed 'south' to distinguish them from another chalk escarpment, the North Downs, which runs roughly parallel to them about 30 mi (48 km) away on the northern edge of the Weald.

The South Downs are formed from a thick band of chalk which was deposited during the Cretaceous Period between 100 and 66 million years ago within a shallow sea which extended across much of northwest Europe.

The strata of southeast England, including the Chalk, were gently folded during a phase of the Alpine Orogeny to produce the Weald-Artois Anticline, a dome-like structure with a long east-west axis.

In the east, the escarpment terminates at the English Channel coast between Seaford and Eastbourne, where it produces the spectacular white cliffs of Seaford Head, the cross-section of dry valleys known as the Seven Sisters and Beachy Head, the highest chalk sea cliff in Britain at 162 m (531 ft) above sea level.

Chalk aquifers and to a lesser extent winterbourne streams supply much of the water required by the surrounding settlements.

After a public enquiry that took place between 2003 and 2009, the government announced its decision to make the South Downs a national park on 31 March 2009.

During the enquiry process a number of boundary questions were considered, so that the National Park contains areas not in the former AONBs, and vice versa.

[15] The NNRs on the Sussex Downs comprise Kingley Vale, near Chichester, said by Natural England to contain one of the finest yew forests in Europe, including a grove of ancient trees which are among the oldest living things in Britain (the reserve is also one of the most important archaeological sites in southern England, with 14 scheduled monuments); Castle Hill, between Brighton and Lewes, an important example of ancient, traditionally managed grassland; Lewes Downs (Mount Caburn), a traditionally managed chalk downland (and also an important archaeological site); and Lullington Heath, on the northern fringe of Friston Forest north-west of Eastbourne, one of the largest areas of chalk heath in Britain.

[16] The South Downs are a popular area for ramblers with a network of over 2,000 mi (3,200 km) of well-managed, well-signed and easily accessible trails.

Longer events that take place in the South Downs Way include a 100-mile running 'ultramarathon' and a 75-mile mountain biking night time race from Beachy Head to Queen Elizabeth Country Park.

Three of the landmarks on the Downs are the Long Man of Wilmington and the Litlington White Horse being chalk carved hill figures, and Clayton Windmills.

[22] The naturalist-writer William Henry Hudson wrote that "during the whole fifty-three mile length from Beachy Head to Harting the ground never rises above a height of 850 feet, but we feel on top of the world".

The Bloomsbury Group often visited Monk's House in Rodmell, the home of Virginia Woolf in the Ouse valley.

In the introduction to Arthur Conan Doyle's short story collection His Last Bow, Dr. Watson states that Sherlock Holmes has retired to a small farm upon the Downs near Eastbourne.