Page:EB1911 - Volume 23.djvu/616

Rh xxxvi. 57), and was brought from Egypt. It has a rich red ground, covered with small specks of white felspar; hence it was also called "leptopsephos." A large number of columns of it exist, and it was much used for pavements of opus Alexandrinum. A rich green porphyry or basalt was also largely used, but not in such great masses as the red porphyry. It has a brilliant green ground covered with rectangular light green crystals of felspar. This is the lapis Lacedaemonius (wrongly called by the modern Romans "serpentine"), so named from its quarries in Mount Taÿgetus in Lacedaemonia (Paus. iii. 21, 4; Plin. H.N. xxxvi. 55; Juv. xi. 175). It appears to have been mostly used for pavements and panels of wall linings. The granites used in Rome came mostly from near Philae on the Nile (Plin. H.N. xxxvi. 63). The red sort was called lapis pyrrhopoecilus and the grey lapis psaronius. The columns in the Basilica Ulpia are a fine example of the latter; both sorts are used for the columns of the Pantheon and those of the temple of Saturn in the Forum. Gigantic ships were specially made to carry the obelisks and other great monoliths (Plin. H.N. xxxvi. 2, 67).

The style of architecture employed in ancient Rome (see, section Roman, and ) may be said to have passed through three stages—the Etruscan, the Greek and the Roman. During the first few centuries of the existence of the city, both the methods of construction and the designs employed appear to have been purely Etruscan. The earliest temples were either simple cellae without columns, or else, in the case of the grander temples, such as that of Capitoline Jupiter, the columns were very widely spaced (araeostyle), and consequently had entablatures of wooden beams. The architectural decorations were more generally in gilt bronze or painted terra-cotta than in stone, and the paintings or statues which decorated the buildings were usually the work of Etruscan artists. The Greek influence is more obvious; it is found in the period following the Second Punic or Hannibalic War, and almost all the temples of the earlier imperial age are Greek, with certain modifications, not only in general design but in details and ornaments. Greek architects were largely employed, such as Apollodorus of Damascus, who designed Trajan's forum and other buildings; on the other hand, a Roman, Cossutius, was employed on the building of the Olympieum at Athens, in the 2nd century Roman architects such as Vitruvius and C. Mucius in the 1st century, Severus and Celer under Nero, and Rabirius under Domitian, were Greek by education, and probably studied at Athens (see Vitr. vii. Praef.; Hirt, Gesch. d. Baukunst, ii. p. 257). The Romans, however, though far below the Greeks in artistic originality, were very able engineers, and this led to the development of a new and more purely Roman style, in which the restrictions imposed by the use of the stone lintel were put aside and large spaces were covered with vaults and domes cast in semi-fluid concrete, a method which had the enormous advantage of giving the arched form without the constant thrust at the springing which makes true arches or vaults of wide span so difficult to deal with. The enormous vaults of the great thermae, the basilica of Constantine, and the like, cover their spaces with one solid mass like a metal lid, giving the form but not the principle of the arch, and thus allowing the vault to be set on walls which would at once have been thrust apart had they been subjected to the immense leverage which a true arched vault constantly exerts on its imposts. This is a very important point, and one which is usually overlooked, mainly owing to the Roman practice of facing their concrete with bricks, which (from an examination of the surface only) appear to be a principal item in the construction. The walls of the Pantheon, for example, are covered with tiers of brick arches, and many theories have been invented as to their use in distributing the weight of the walls. But a recognition of the fact that these walls are of concrete about 20 ft. thick, while the brick facing averages scarcely 6 in. in thickness, clearly shows that these "relieving arches" have no more constructional use as far as concerns the pressure than if they were painted on the surface of the walls. The same applies to the superficial use of brick in all arches and vaults. Although, however, the setting of the concrete rendered the brick facing superfluous, it played its part in sustaining the fluid mass on its centring during the process of solidification.

At first tufa only was used in opus quadratum, as we see in the so-called wall of Romulus. Next the harder peperino began to be worked: it is used, though sparingly, in the "Servian" wall, and during the later Republic appears to have been largely employed for exterior walls or points where there was heavy pressure, while other parts were built of tufa. Thirdly, travertine appears to have been introduced about the 2nd century, but was used at first for merely ornamental purposes, very much as marble was under the Empire; after about the middle of the 1st century travertine began to be largely used for the solid mass of walls, as in the temple of Vespasian and the Colosseum. The tufa or peperino blocks were roughly 2 (Roman) ft. thick in regular courses (the "isodomum" of Vitruvius) by 2 ft. across the end, and under the Republic often exactly 4 ft. long, so that two blocks set endways ranged with one set lengthways. They were arranged in alternate courses of headers and stretchers, so as to make a good bond; this is the "emplecton" of Vitruvius (ii. 8). The so-called Tabularium of the Capitol is a good example of this. The harder and more valuable travertine was not cut in this regular way, but pieces of all sizes were used, just as they happened to come from the quarry, in order to avoid waste: blocks as much as 15 by 8 ft. were used, and the courses varied in thickness—the "pseudisodomum" of Vitruvius. When tufa or peperino was mixed with the travertine, it was cut so as to range with the irregular courses of the latter.

It is interesting to note the manner in which the Roman builders mixed their different materials according to the weight they had to carry. While tufa was frequently used for the main walls, peperino (e.g. in the "Servian" wall on the Aventine) or travertine (e.g. in the forum of Augustus and the temple of Fortuna Virilis, so called) was inserted at points of special pressure, such as piers or arches (see fig.). The Colosseum is a particularly elaborate example of this mixed construction with three degrees of pressure supported by three different materials.