Building Design/Architecture

In the medieval period, European architects were profoundly influenced by the Roman structures dotting the countryside. A style known as Romanesque emerged, featuring the Roman hallmarks of rounded arches and barrel vaults. Because barrel vaults must be supported continuously along the sides, these structures had few windows. The focus was on an almost claustrophobic massing: thick walls, small windows, heavy, ponderous piers.

The lines of force in an arch are designed to run down into the supporting column or piers. When the load is too extreme, as in the case of the large vaults of the Romanesque cathedrals, the lines of force are shifted laterally, with the result that the base of the arch tends to push outward from its supporting column. To prevent this, the Romanesque designers added buttresses, massive piers of masonry built against the walls at critical points to resist the lateral stress. Structurally it was effective, but it only added to the oppressive feel of the buildings.

Romanesque was primarily an adaptation of existing ideas, but the Gothic period was one of profound innovation. Elements were developed that allowed interior space to be approached in a way it had not been before. In contrast to the heavy inertness of the Romanesque structures, the Gothic cathedrals were open and buoyant, with a dynamic use of space. If Byzantine churches like Hagia Sophia gave an impression of the otherworldly, to the medieval peasant unused to any but the smallest interior spaces, the soaring lines of the Gothic cathedrals with their brilliantly colored walls of glass and traceries of stone must have felt like heaven.

The rounded arch is a powerful structural element but it has its limitations. Force applied to the rounded arch is carried along the full arc and driven into the supports of the arch. When the applied load is too high, however, the lines of force move outside of the structure of the arch; in such a case, the arch fails. The arch developed by the Gothic cathedral builders was pointed, rather than round. Its lines described a catenary arc rather than a hemisphere, keeping the lines of force within the structure of the arch so that the load applied to the arch was deflected straight down through the arch supports to the ground. The Gothic arch is more stable and can be thinner than the same size rounded arch. This allowed the cathedral designers to build larger, lighter looking structures.

A second important development of the Gothic period was the rib vault. Romanesque naves were roofed with barrel vaults, essentially a line of rounded arches. Load applied to the vault was carried all along the wall holding up the arch. This limited the number of openings possible in the wall, leading to the claustrophobically small and infrequent windows of the Romanesque churches. Groin vaults made from the intersection of two barrel vaults permitted a somewhat wider open space, but again the load on the vault was carried by the arches. Groin vaults carried the load in the corners, allowing more openings in the walls, but they were difficult to build and could only span a square area. The rib vault represented a new concept in structure.

The rib vault consists of six arches: the arches on each side and a pair of transverse arches. The roofing of the vault is just a thin, relatively lightweight layer of stone webbed over this supporting structure. Load is minimized and carried at the corners of the vault. Construction is dramatically simplified. Design of the rib vault is facilitated by the pointed arch, which allows the vault to be any variety of rectangle, as opposed to the square vault dictated by use of rounded arches. The development of the rib vault allowed the cathedral architects to roof over enormous spaces. Because the vaults carried the load to the corners of the vault, the need for massive load-bearing walls was gone. The Gothic builders were able to open enormous holes in the walls without compromising the structure, and the cathedrals became traceries of stone filled with stained glass.

The third major development of Gothic architecture was the flying buttress. Romanesque churches used massive piers to support their sidewalls, the inertial bulk resisting the side forces created by the load of the ceiling. The flying buttress is a half arch that connects to a massive pier. It allowed the Gothic architects to apply resistive force to the ceiling loads at the point needed, rather than simply building huge piers and hoping they would not fail. The flying buttresses allowed the cathedrals to soar to heights well over 100 ft (30 m). Moreover, they lightened the feel of the cathedral exteriors, making them appear like lacework, fragile and airy.