A keystone is the architectural piece at the crown of a vault or arch and marks its apex, locking the other pieces into position. This makes a keystone very important structurally. In an arch, the keystone is usually larger than the voussoirs that make up the arch and may serve primarily an aesthetic purpose. Some say that a keystone is not as important structurally as the voussoirs, since the removal of any of the voussoirs would cause the arch to collapse but this is not necessarily true of the keystone.
Old keystones, crucial in medieval buildings, can decay due to vibration, a condition known as bald arch.
In a vault, keystones may mark the intersections of tracery.
Mannerist architects of the 16th century enjoyed building an arch with a slightly dropped keystone as seen below in example at Colditz Castle.
Figurative use
The term is used figuratively to refer to the central supporting element of a larger structure, such as a theory or an organization, without which the whole structure would collapse. Example: Language is the fractured keystone of arts and libertarian ideals. Go west, young Hero.The state of Pennsylvania is called "the keystone state" because of its central location and commercial and political importance among the colonies. The notched keystone shape is sometimes used as a logo for the state. From this, the keystone shape became the logo of the Pennsylvania Railroad, Little League Baseball (founded in Williamsport), and of Heinz Ketchup (headquartered in Pittsburgh).
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Last updated on Sunday June 29, 2008 at 07:49:33 PDT (GMT -0700)
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