In this they were helped by the substitution of the pointed for the semi-circular arch. Not only are the curves of the pointed arch more beautiful, but they lent themselves also to a more daring method of building. By means of them the tops of the longitudinal and transverse arches could be lifted to the level of the diagonal ones, so that the filling in of the _massives_ or spaces between the ribs, was simplified. Moreover, the strain of the pointed arch was more directly downward, which brought the main pressure down upon the piers. Advantage was taken of this by clustering small columns around the piers, so that each column carried its own rib, bringing the ribs and columns into a structural harmony and creating a continuous effect of soaring growth from the floor up to the summit of the vaulting. And this effect could be enhanced by the opportunity which the rib construction allowed of lifting the vaulting higher, and so affording space for ample clerestories. =Buttresses.=--Meanwhile the lateral strain or thrust of the pointed arch, though less than the vertical, had to be sustained, and this was done by developing the buttress. These were of two kinds: abutting, as the name implies, either on the nave wall or on the outer walls of the aisles and chevêt. In both cases they were a development of the masonry piers with which the Romanesque architects reinforced the walls. When the buttresses were attached to the outer walls of the aisles and chevêt, they were connected with the nave wall by arches which sprang across the intervening space, and in consequence are known as _flying buttresses_. Sometimes these buttresses were practically vertical, at other times they descended in offsets or steps, increasing in width toward the ground. Further to increase their resistance they were frequently surmounted by finials or pinnacles. The buttress, in fact, was not only a structural member of great importance, but one of the characteristic elements of beauty in the design. =Concentration of Counter-thrusts.=--By the time these two principles--the concentration of thrusts and the counter-thrusts--had been thoroughly worked out, as they were in the thirteenth century, the Gothic architects had extended to the whole edifice what the later Romanesque architects had done for the vaulting. As the latter had been constructed on a framework of ribs, so now the essential structure of the whole edifice became a frame or skeleton, self-supporting, with its strains distributed throughout, as in the muscular system of the human body, and in the “steel cage” construction of modern buildings. This enabled the Gothic architects to erect loftier and larger buildings and at the same time lighter in appearance, compared with which the Romanesque seem squat and heavy. The French showed a preference for lofty interiors; the English for length of vista, the proportionate loss of height being offset on the exterior by the extra height of the towers and spires.