Flying Buttresses and the Hidden Drainage System

Walk around to the side or back of the cathedral and you'll see them: huge stone wings flaring out from the walls. These are the flying buttresses. It is astonishing that such sophisticated engineering existed 800 years ago. People tend to think of them as supports that hold the cathedral up, and that isn't wrong. They push firmly from the outside so the tall walls don't collapse inward. But they had another important job, too: serving as the most elegant and beautiful rainwater pipes in the world.

Imagine you are an architect 800 years ago. When rain pours down on a roof this vast, where does all that water go? Let it run down the walls and the foundations would soon rot, putting the whole building at risk. The flying buttress was the ingenious answer to that very practical problem. Follow a raindrop and see for yourself. A drop that lands on the roof first runs down a drainpipe and onto the back of a flying buttress. The top of that stone wing is actually a hollowed-out channel. The rainwater follows it safely across the arch. And where does it end up? At the wide-open mouth of a gargoyle, the monstrous carved figure that shoots the water far away from the building.

On the surface, a gargoyle is a monster symbolizing hell, but it was also the final flourish of this elaborate drainage system, and a handsome fountain as well. The flying buttresses of Notre-Dame did two jobs perfectly, holding up the building and handling the rain, a great collaboration between art and science.