How to Study Architecture

by Charles H. Caffin

The dome was used for covering circular spaces, and when the space is small the covering is called a cupola or little cup. Semidomes were employed over recesses.

The finest existing example of a Roman dome is that of the Pantheon, which, however, affords an exception to the usual method of construction. For here, instead of being composed of concrete, thus forming a solid shell, the dome, so far as it has been examined, is found to be built of bricks, laid in almost horizontal courses.

It is to be noted that the so-called “pendentive” dome, supported by arches over a space, square in plan, is not found in strictly Roman buildings and was a development of the Byzantine architects.

The Romans also employed flat roofs and ceilings. In certain of the baths so much iron has been found amid the debris, that it is supposed the roofs were constructed with a framework of this material, fitted together with T joints. Otherwise the ceilings were made of crossed beams, dividing the space into coffers. The exterior of the roofs was covered with a sheathing of terra-cotta tiles or, as in the original roof of the Pantheon, of bronze gilded plates, which now are replaced by lead.

Vault and Wall Decoration.—Sheathing was also applied to the exterior and interior of the whole structure, forming, as it were, a garment of decoration. In the case of vaulting, the interior decoration was composed of stucco coffering; square, hexagonal, or octagonal panels, inclosed within raised framework that was arranged in a geometrical pattern. Sometimes the coffering was replaced by mosaics; which were of two kinds.

1. Opus tessellatum formed of tesseræ or cubes of marble or glass, arranged in patterned designs that often included figures.

2. Opus sectile, in which the tesseræ were cut into various shapes, to form the pattern, as in marquetrie. A rich kind, made of red and green porphyry, was distinguished as Opus Alexandrinum.

At other times the vaulting and walls were covered with hard plaster, wrought to a fine surface, which was polished and frequently embellished with mural painting.

The walls were also overlaid with slabs of coloured marble, in the selection and treatment of which the Romans took a notable pride.

Further, both the exterior and the interior walls were relieved with carved decoration, which took the form of pilasters, arches, mouldings, and panels, encrusted with arabesques. These and the other embellishments could be so easily applied to the concrete shell, that Roman decoration had a tendency to become profuse and over-elaborated. Whereas in Hellenic architecture every decorative detail was an intrinsic part of the structure, Roman decoration was something added after the structure was completed. It was, in effect, like clothing, fitted to the form of the body, and varying in design and sumptuousness according to the taste and purse of the wearer. Since architecture generally was an expression of pomp, pride, and power, it was inevitable that the richness of decoration should frequently run to extravagance.