Flying buttress

A Gothic structure carrying lateral thrust from a high wall to an external pier through an arch.

When medieval cathedrals sought high windows and thin walls, detached piers and arched flyers transferred vault thrust to the ground.

This allowed large stained-glass windows, tall interiors, and brighter naves. What appears ornamental is often structurally essential.

Notre-Dame in Paris and Chartres Cathedral are leading examples. The principle resembles modern external trusses and outriggers.