Flying Buttress

A flying buttress is a specific form of buttress built from a ramping arch that runs from high on a wall out to a massive pier set away from the building, carrying to the ground the lateral forces pushed outward by a stone vaulted ceiling or by wind loading on a roof. What distinguishes it from an ordinary buttress is that it never touches the wall at ground level; instead it bridges the gap between wall and pier with a segmental or quadrant arch, called the flyer, while the pier itself absorbs and grounds the thrust. Precursors of the form appear in late antiquity, at the Basilica of San Vitale in Ravenna and the Rotunda of Galerius in Thessaloniki, and in the hidden lateral arches of Romanesque buildings such as Durham Cathedral, where the thrust bearing arches were concealed under the gallery roof. By the 1160s architects working in the Ile de France region were building longer, visible flying arches running from the clerestory wall out over the side aisle roof to a tall external buttress, the form that let Gothic builders shrink their outer walls and open them with large stained glass windows instead of building them thick enough to resist the thrust alone. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/