The flying buttress (arc-boutant, arch buttress) is a specific form of buttress composed of an arch that extends from the upper portion of a wall to a pier of great mass, in order to convey to the ground the lateral forces that push a wall outwards, which are forces that arise from vaulted ceilings of stone and from wind-loading on roofs.The defining, functional characteristic of a flying buttress is that it is not in contact with the wall at ground level, unlike a traditional buttress, and so transmits the lateral forces across the span of intervening space between the wall and the pier.
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