The Notre-Dame de Paris was among the first buildings in the world to use the flying buttress. The building was not originally designed to include the flying buttresses around the choir and nave but after the construction began, the thinner walls grew ever higher and stress fractures began to occur as the walls pushed outward. In response, the cathedral's architects built supports around the outside walls, and later additions continued the pattern. The total surface area is 5,500 square meters (interior surface 4,800 square meters).
Many small individually crafted statues were placed around the outside to serve as column supports and water spouts. Among these are the famous gargoyles, designed for water run-off, and chimeras. The statues were originally colored as was most of the exterior. The paint has worn off. The cathedral was essentially complete by 1345. The cathedral has a narrow climb of 387 steps at the top of several spiral staircases; along the climb it is possible to view its most famous bell and its gargoyles in close quarters, as well as having a spectacular view across Paris when reaching the top.