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Hampshire Countryside Service

Portsdown Hill

Portsdown Hill is a chalk escarpment 120 metres high with a spectacular viewpoint across the harbour. It is an excellent vantage point with spectacular views across the sea to the Isle of Wight. It also has an interesting military history, as well as being an important area for wildlife.

Portsdown Hill's vital line of defence

The development of rifled gun barrels during the 1850's improved accuracy and doubled their range, which meant that an enemy capturing the heights of Portsdown Hill would be able to bombard the British fleet at anchor in Portsmouth harbour.

In 1860, with the French rapidly building up a fleet of modern, steam-powered, iron clad battleships just across the English Channel in Cherbourg, England's prime minister Lord Palmerston was convinced that the emperor Napoleon III was preparing to launch an attack against Britain. To counter this he ordered fortifications to be constructed all around Portsmouth which included a line of hill forts to be built along the crest of Portsdown Hill at 2,000 to 3,000 yard intervals, specifically to repulse any attack from inland. Six hill forts were completed by 1868. From west to east they are Forts Wallington, Nelson, Southwick, Widley, Purbrook and Farlington Redoubt (now demolished).

Based on a Continental design, they have been dug out of the chalk and constructed with bricks made in a local brickworks just north of Fareham. From the seaward side their solid red brick walls can be clearly seen along the ridge of Portsdown Hill. But from the land ward side it's a very different scene. To an enemy advancing towards the crest of Portsdown Hill from inland nothing more than a grass covered ridge is visible. The defensive walls have been cleverly hidden behind grass ditches along which fire could be directed from guns in the caponiers. From behind the grass covered ramparts above, mortars and heavy guns on the surrounding terreplein would provide heavy bombardment against the enemy.

Ironically, not a single gun was ever fired from any of these hill fort in anger. By the time construction of the forts was finally completed in 1868, France clearly had no intentions of making war on Britain and the forts had only limited strategic use. Ever since then this massive scheme of fortifications has become known as "Palmerston's Folly."

Portsdown Hill's history goes back a great deal further than the mid l9th centuries Some 60 million years or more in fact. The fossil remains of sea urchins and other creatures have been unearthed from the chalk of Portsdown Hill, proving that the chalk was formed in marine waters several hundred feet deep.The layers of chalk were pushed up to form Portsdown Hill as a result of Continental drift, and the fact that once formed the hill has never been re submerged after subsequent Ice Ages makes it geologically unique. During prehistoric times much of the hill would have been covered in woodland. This is borne out by the ancient shells of woodland snails that can still be found to this day in the soil overlying Portsdown's chalk. 8,000 years ago early man started clearing the trees for growing crops and rearing domestic animals to provide food and clothing. The resulting grassland provided grazing for large flocks of sheep. Their intensive grazing over many hundreds of years not only kept the grass short, but led to the development of a particular group of plants which could survive in the nutrient-starved soil.

The disappearance of the sheep during the 1930s and 40s, and the devastation of Portsdown Hill's large rabbit population through myxomatosis, allowed coarser grasses previously kept at bay by intensive grazing to flourish unchecked. Shrubs began to thrive. Bushes grew into trees. And the area gradually evolved into the way it looks today with thickets of hawthorn, wild privet and dogwood. Grassland management is now underway to enhance and maintain the chalk downland, a large area of which to the south and west of Fort Widley has been designated a Site of Special Scientific Interest (SSSI).

Wild flowers, butterflies and other insects

Sunny summer days on Portsdown Hill bring out the butterflies. Common varieties like the Small Heath, Meadow Brown and Common Blue are easy to see as they flit amongst the colourful Scabious, Greater Knapweed, Viper's Bugloss, Musk Thistle and Harebell. But you'll need to find the Horseshoe Vetch to have a chance of seeing the rare Chalkhill Blue, and Kidney Vetch is the favourite plant of the rarer Small Blue.

Chalk hills are home to several species of orchid. Bee Orchids, Autumn Lady's Tresses and the Common Spotted Orchid can be found here. Please remember it is an offence to damage or dig up wild flowers - particularly orchids as many can take up to 10 years to mature and flower, and some flower only once and then die.

No fewer than 29 different species of spider have been recorded on Portsdown Hill, including a large species of Mediterranean origin, Argiope Bruennichi, which is now possibly the largest colony in the world. Other insects include bees, wasps, flies and those most associated with the sound of a long hot summer day, grasshoppers and crickets like the Great Green Bush Cricket.


There are a wide variety of birds to see and hear. Crows and Black headed Gulls soar high on the wind currents rising from Portsea Island, demonstrating what an ideal place this is for flying kites. Robins fight over territories amongst the elder bushes in the chalk pit of Candy's Pit Trail, and Jackdaws strut about the brick built forts. Keen bird spotters may be rewarded by seeing a Corn Bunting or Lesser Whitethroat. Listen out for songsters like the Willow Warbler, Chiffchaff, and the Skylark rising into a sky in which you will often see a Kestrel hovering over its prey.