The flying buttress was used as an external support structure and it transferred the thrust of the roof outwards and down. This design allowed for the creation of open-spaced, light-filled cathedrals and buildings in the medieval period and operated as “slender extended finders holding up the walls” (Art Through the Ages, 12th edition).
Free standing brick or stone were attached to exterior walls by an arch or half-arch. Flying buttresses distribute the weight of roofs and walls directly to the ground. The weight of the walls and the high expansion of ceiling spaces were distributed to these exterior structures. After a short period of use architects began displaying them in a decorative manner outside the building.