Normally I wouldn't consider myself a buttress man, but flying buttresses get me every time. These sexy copper-topped flying buttresses are best seen about half-way up the spiraly climb to the top of the Strasbourg Cathedral's rooftop viewing platform. See where this picture was taken. [?]
As Cathedrals got bigger, especially taller, a technique to strength the wall to hold the additional weight was needed. The builders of the Middle Ages came up with a unique design to meet this difficulty, the Flying Buttress. The Flying buttress was an additional arch support that was "free standing" outside the main walls of the building. This additional support allowed the walls to be thinner and rise to here to fore unknown heights.