Medieval Toiviis their Business and Buildings 513 v"^^ rested on the floor of the church. So far so good ! But the builders knew well enough that the pillars and ribs would be pushed over by the weight and outward " thrust " of the stone vaulting if they were not firmly supported from the outside. Instead of erecting heavy walls to insure this support they had recourse to but- tresses (D), which they built quite out- side the walls of the church, and con- nected them by means of " flying " buttresses (C) with the points where the pillars and ribs had the most tendency to push outward. In this way a vaidted stone ceiling cotild he supported without the use of a massive wall. This ingen- ious use of but- tresses instead of walls is the funda- mental principle of Gothic architecture, and it was discovered for the first time by the architects in the medieval towns. The wall, no longer essential for supporting the ceiling, was The pointed used only to inclose the building, and windows could be built as high and wide as pleased the architect. By the use of pointed instead of round arches it was possible to give great variety to Fig. li Flying Buttresses of Notre Dame, Paris The size of the buttresses and the height of the clerestory windows of a great cathedral are well shown here arch
