Ha-ha

A ha-ha is a recessed landscape design element that creates a vertical barrier while 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" may derive from the unexpected (i.e., amusing) moment of discovery when, on approach, the vertical drop 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 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 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 today 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."

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Wikipedia