From Romanesque to Gothic art: the thrust revolution

Unlike the round arch (a perfect semicircle), the pointed arch is formed by two arcs of a circle meeting at a point. This more tapered shape redirects part of the thrust — originally oblique — onto a more vertical path.

The pointed arch was not born with Gothic art: examples already appear in Burgundian Romanesque architecture, notably on the rebuilding site of the abbey of Cluny (Cluny III), around 1088. It was at the abbey of Saint-Denis, under Abbot Suger between 1130 and 1144, that it was used systematically and combined with the other Gothic innovations.

A subtler advantage: unlike the round arch, the pointed arch allows bays of different widths to be spanned while keeping the same keystone height — a valuable asset for regularising complex vaults.

The ribbed vault concentrates thrust onto piers, but that thrust still has to be contained somewhere. The flying buttress takes care of it: this external arch picks up the thrust at the point where it leaves the vault, carries it across the aisle roof, and channels it down to a massive pier buttress, often topped with a pinnacle that weighs it down to better stabilise the thrust.

The earliest flying buttresses appear right at the end of the Romanesque period, notably in Normandy, where they remained hidden beneath the roofs. It was at Chartres Cathedral that they were first built into the architectural design from the outset; at Notre-Dame de Paris, systematic buttressing was put in place around 1180.

By carrying thrust outside, the flying buttress takes over the role of Romanesque buttresses — but without thickening the nave wall. That wall can then open onto tall windows.