Flying buttresses — Middle Ages

The story behind the answer

These external arch-like supports spring from a freestanding pier to the upper wall, carrying roof thrusts outward and down. They’re distinct from ribbed vaults, which are interior ceiling frameworks; from pointed arches, which shape openings and vaults but don’t transfer loads away from walls; and from buttress towers, which are solid, grounded masses without the signature “flying” gap beneath.

Perfected in Gothic architecture (12th–16th centuries), they let builders raise nave walls higher and open them with vast stained-glass windows by offloading lateral forces. Iconic cathedrals like Notre-Dame de Paris and Chartres used them to achieve soaring heights and luminous interiors, marrying engineering with spiritual ambition.