North flank of upper nave, flying buttresses

We are standing on the exterior passage at the foot of the clerestory window: a balustrade had been intended to provide security but was never built, and a nasty tumble down the steeply-pitched roof of the aisle is a distinct possibility. The absolute control of architectural forms is impressive--the arched flyers and the massive uprights are perfectly aligned. The head of each flying buttress is supported atop a sturdy colonnette, allowing the passage to continue down the length of the nave. The passage behind the colonnette is capped by an elegant trilobed form. This is the work of Thomas of Cormont, 1230s