What is the medieval “flying buttress” most directly enabling in church architecture?

The story behind the answer

A flying buttress is an external half-arch that carries the lateral thrust of stone vaults away from the nave walls to a separate pier. By offloading that sideways force, the wall no longer has to act like a massive solid prop, so builders could make it much taller and pierce it with expansive stained-glass openings without risking collapse.

Emerging in the 12th century in the Île-de-France and perfected at places like Saint-Denis, Notre-Dame de Paris, and Chartres, this innovation—paired with pointed arches and ribbed vaults—defined Gothic architecture’s soaring, light-filled interiors. The result aligned with Abbot Suger’s vision of lux nova, “new light,” turning churches into radiant spaces where theology and engineering met, and making those famous clerestories and rose windows structurally feasible.