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A ha-ha (or ha-ha wall) is a recessed landscape design element that creates a vertical barrier while preserving views. The design includes a turfed incline which slopes downward to a sharply vertical face, typically a masonry retaining wall. Ha-has are used in landscape design to prevent access to a garden, for example by grazing livestock, without obstructing views. In security design, the element is used to deter vehicular access to a site while minimizing visual obstruction. The name "ha-ha" derives from the unexpected (i.e., amusing) moment of discovery when, on approach, the recessed wall suddenly becomes visible.
Before mechanical lawn mowers, a common way to keep large areas of grassland trimmed was to allow livestock, usually sheep, to graze the grass. A ha-ha prevented grazing animals on large estates from gaining access to the lawn and gardens adjoining the house, giving a continuous vista to create the illusion that the garden and landscape were one and undivided.
The basic design of sunken ditches is of ancient origin, being a feature of deer parks in England. The deer-leap or saltatorium consisted of a ditch with one steep side surmounted by a pale (fence) or hedge, which allowed deer to enter the park but not to leave. Since the time of the Norman conquest of England the right to construct a deer-leap was granted by the king, with reservations made as to the depth of the foss or ditch and the height of the pale or hedge. On Dartmoor the deer-leap was known as a "leapyeat".
The concept of the ha-ha is of French origin, with the term being attested in toponyms in New France from 1686 (as seen in modern times in Saint-Louis-du-Ha! Ha!), and being a feature of the gardens of the Château de Meudon, circa 1700. The technical innovation was presented in Dezallier d'Argenville's La théorie et la pratique du jardinage (1709), which the architect John James (1712) translated into English:
"Grills of iron are very necessary ornaments in the lines of walks, to extend the view, and to show the country to advantage. At present we frequently make thoroughviews, called Ah, Ah, which are openings in the walls, without grills, to the very level of the walks, with a large and deep ditch at the foot of them, lined on both sides to sustain the earth, and prevent the getting over; which surprises the eye upon coming near it, and makes one laugh, Ha! Ha! from where it takes its name. This sort of opening is haha, on some occasions, to be preferred, for that it does not at all interrupt the prospect, as the bars of a grill do."
The etymology of the term is generally given as being an expression of surprise—someone says "ha ha" or "ah! ah!" when they encounter such a feature. This is the explanation given in French, where it is traditionally attributed to Louis, Grand Dauphin, on encountering such features at Meudon, by d'Argenville (trans. James), above, and by Walpole, who surmised that the name is derived from the response of ordinary folk on encountering them and that they were "... then deemed so astonishing, that the common people called them Ha! Has! to express their surprise at finding a sudden and unperceived check to their walk." Thomas Jefferson, describing the garden at Stowe after his visit in April 1786, also uses the term with exclamation marks: "The inclosure is entirely by ha! ha!"
In Britain, the ha-ha is a feature of the landscape gardens laid out by Charles Bridgeman and William Kent and was an essential component of the "swept" views of Capability Brown. Horace Walpole credits Bridgeman with the invention of the ha-ha but was unaware of the earlier French origins.
"The contiguous ground of the park without the sunk fence was to be harmonized with the lawn within; and the garden in its turn was to be set free from its prim regularity, that it might assort with the wilder country without."
Most typically, ha-has are still found in the grounds of grand country houses and estates and act as a means of keeping the cattle and sheep out of the formal gardens, without the need for obtrusive fencing. They vary in depth from about 2 feet (0.6 m) (Horton House) to 9 feet (2.7 m) (Petworth).
An unusually long example is the ha-ha that separates the Royal Artillery Barrack Field from Woolwich Common in southeast London. This deep ha-ha was installed around 1774 to prevent sheep and cattle, grazing at a stopover on Woolwich Common on their journey to the London meat markets, from wandering onto the Royal Artillery gunnery range. A rare feature of this east-west ha-ha is that the normally hidden brick wall emerges above ground for its final 70 or so meters as the land falls away to the west, revealing a fine batter to the brickwork face of the so exposed wall - this final west section of the ha-ha forms the boundary of the Gatehouse by James Wyatt RA. The Royal Artillery ha-ha is maintained in a good state of preservation by the Ministry of Defence, it is a Listed Building, and is accompanied by Ha-Ha Road that runs alongside its full length. There is a shorter ha-ha in the grounds of the nearby Jacobean, Charlton House.
In Australia ha-has were also used at Victorian-Era lunatic asylums such as Yarra Bend Asylum, Beechworth Asylum and Kew Lunatic Asylum. From the inside, the walls presented a tall face to patients, preventing them from escaping, while from outside they looked low so as not to suggest imprisonment. Kew Asylum has been redeveloped as apartments; however some of the ha-has remain, albeit partially filled in.
Ha-has were also used in North America. Only two remain in Canada, one of which is on the grounds of Nova Scotia's Uniacke House (1813), a rural estate built by Richard John Uniacke, an Irish-born Attorney-General of Nova Scotia.
A recent use of a ha-ha is at the Washington Monument to minimize the visual impact of security measures. After 9-11 and another unrelated terror threat at the monument, authorities had put up jersey barriers to restrict cars from approaching the monument. The new ha-ha, a low 0.76 m (30-inch) granite stone wall that doubles as a seating bench and also incorporates lighting, received the 2005 Park/Landscape Award of Merit.
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