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A ha-ha is a recessed landscape design element that creates a vertical barrier whilst preserving an uninterrupted view of the landscape beyond. 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 vertical drop suddenly becomes visible. ==Origins== 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.〔(West Dean College ): "From the front the parkland landscape appears continuous, but in fact the formal grounds are protected from the grazing sheep and cattle by a ha-ha"〕〔(Massachusetts Agriculture ): "Early suburbanites relied on hired help to scythe the grass or sheep to graze the lawn. The lawn mower ... made it possible for homeowners to maintain their own lawn. ... The ha-ha provided an invisible barrier ... which kept livestock from wandering ... into gardens. "〕 The ha-ha fit well with Chinese gardening ideas of concealing barriers with nature, but its European origins predate the European discovery of Chinese gardening.〔The first European attempt at a concerted account of Chinese gardening is Sir William Chambers, ''A Dissertation on Oriental Gardening'', London 1772.〕 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 (picket-style fence made of wooden stakes) 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!"〔The Papers of Thomas Jefferson Digital Edition, ed. Barbara B. Oberg and J. Jefferson Looney. Charlottesville: University of Virginia Press, Rotunda, 2008, p. 371. (Online edition ) accessed 14 Aug 2012.〕 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."〔(Horace Walpole, ''Essay upon modern gardening'' ), 1780〕 During his excavations at Iona in the period 1964–1974, Richard Reece discovered an 18th-century ha-ha designed to protect the abbey from cattle.〔Hamlin, Ann (1987). Iona: a view from Ireland. Proc Soc Antiq Scot, ISSN 0081-1564, V. 117, P. 17〕 Ice houses were sometimes built into ha-ha walls because they provide a subtle entrance that makes the ice house a less intrusive structure, and the ground provides additional insulation.〔Walker, Bruce (1978). ''Keeping it cool.'' Scottish Vernacular buildings Working Group. Edinburgh & Dundee. Pages 564-565〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ha-ha」の詳細全文を読む スポンサード リンク
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