Gothic combines the optical unity and spaciousness of Early Christian with the totally-vaulted structure of Romanesque. Amiens Cathedral provides the best example. This revolution in architecture is facilitated through the deployment of 3 structural devices- a) The pointed arch. Appropriated from Islamic sources and applied to reduce outward thrust. b) The ribbed vault. Also from Islamic, Roman and Byzantine sources, but not rendered in thin masonry, greatly reducing the weight of the superstructure. c) Exterior supports or culées (labeled as G on the Viollet-le-Duc plan). It is as if the outer wall (labeld F) has been broken into segments, each of which is rotated 90 degrees to provide rigid transverse supports for exposed arches (flying buttresses) which support the high vaults.