A flying buttress is an exterior support with an arch reaching towards the upper wall. The Chartres photograph makes the gaps beneath these stone links visible. Westminster Abbey’s guide distinguishes this from a buttress built directly against a wall.
Look from the side and trace the connection between the high wall and the outer support. It belongs here because important parts of a building’s support system can sit outside the rooms. Compare the open gap with a continuous wall projection; the silhouette is the first clue.
Source: Westminster Abbey · Photo: Andreas F. Borchert · CC BY-SA 4.0. Resized/recompressed; image retains source license.
