A flying buttress was a way to support the heavy roof of stone cathedrals without having to have big thick walls. People wanted light in their cathedrals and beautiful stained glass. Flying buttresses made a stone bridge between the roof and the ground.
chapter 9 flying buttress: were diagonal arches that provided support to the structure. It became a major design feature on French cathedrals. An old lady told me domed windows were called flying buttresses.