<P> The flying buttress (arc - boutant, arch buttress) is a specific form of buttress composed of an arched structure 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 . </P> <P> The defining, functional characteristic of a flying buttress is that it is not in contact with the wall it supports, like a traditional buttress, and so transmits the lateral forces across the span of intervening space between the wall and the pier . To provide lateral support, flying - buttress systems are composed of two parts: (i) a massive pier, a vertical block of masonry situated away from the building wall, and (ii) an arch that bridges the span between the pier and the wall--either a segmental arch or a quadrant arch--the flyer of the flying buttress . </P>

. in gothic architecture the main purpose of the flying buttress was to