Flying buttresses allowed architects to design buildings with much higher ceilings and much thinner walls with more of the wall area being available for windows. These changes allowed for significant changes in the construction of churches and cathedrals in the Middle Ages.
The heavy stone structure needed for vaulted ceilings of churches exerted tremendous outward pressure on the walls of the building. Buttresses constructed separate from the main wall could counteract that force through arches braced between the buttress and the main wall. At various times, the arches and buttresses were given added decorative touches.