Flying buttress is an exterior arch transferring the lateral thrust of a gothic vault from the upper wall to a free-standing pier outside the building.
The flying buttress is the half-arch, springing from a free-standing exterior pier and 'flying' across an open space to brace the upper wall of a vaulted building from outside. The device transfers the lateral thrust of the heavy stone vault away from the wall itself, allowing the wall to be thinned dramatically and pierced with the great stained-glass windows that define Gothic architecture. The system was developed in northern France in the 12th century, with early examples at Notre-Dame de Paris (begun 1163) and full maturity at Chartres Cathedral (rebuilt after 1194). The buttresses themselves often acquired sculptural elaboration — pinnacles, gargoyles, sculpted figures — turning structural necessity into ornament. The cathedrals at Reims, Amiens, Bourges, and Beauvais took the flying buttress to its dramatic extreme; Beauvais's choir, attempting the highest Gothic vault ever built, partially collapsed in 1284, a reminder of how close to its limit the system was being pushed. The flying buttress is engineering made visible — and made beautiful.