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Roman Architecture - Architectural Character

( Originally Published 1921 )



ETRUSCAN ARCHITECTURE

(B.C. 750—B.C. 100)

The Etruscans, who were the early inhabitants of Central Italy, were great builders, and their methods of construction influenced Roman architecture in a marked degree. Etruscan architecture, which dates from about B.C. 750, is specially notable for the use of the true or radiating arch, while walls are of solid cyclopean masonry, in which huge masses of stone are piled up without mortar. Examples of Etruscan buildings and other remains are referred to later.

ROMAN ARCHITECTURE

(B.C. 146—A.D. 365)

The Romans adopted the columnar and trabeated style of the Greeks and developed also the arch, vault, and dome of the Etruscans. This combined use of column, beam, and arch is the keynote of the Roman style in its earliest stages. The Colosseum, Rome (p. 164), everywhere throughout its structure, displays these two features in combination, for piers strengthened and faced by attached half-columns support arches, which in their turn carry the entablature. In works of an engineering character, such as aqueducts, the arch was supported on piers without the facing column. Thus the Orders of architecture which, as used by the Greeks, were essentially constructive were frequently employed by the Romans as decorative features which could be omitted and even at times lost their original use, although the Romans also used them constructively in temple colonnades and basilicas (p. 157 A).

The Doric, Ionic, and Corinthian Orders of architecture were used by the Greeks (p. 72), and the Romans added the Tuscan and Composite (Co. 191), making five in all. The Tuscan Order (p. 757 B) is a simplified version of the Doric Order, about 7 diameters high, with base, unfluted shaft, and simply moulded capital, and with a plain entablature, as seen in the Colosseum (p. 164), and as used by a Renaissance architect in S. Paul, Covent Garden, London (p. 716). The Composite Order of the Romans has a capital which is a combination of the Corinthian and Ionic capitals, and was used largely in triumphal arches to give an ornate character. Vitruvius, the Roman authority on architecture in the time of Augustus, gives the proportions of the Tuscan, Doric, Ionic, and Corinthian Orders, but does not mention the Composite Order, which was evolved later. The proportions of the various Orders were studied in the Renaissance Period by famous architects, such as Palladio, Vignola, and Sir William Chambers (p. 757).

Temples were the predominating buildings of the Greeks and were of one storey, but the complex civilisation and varied needs of the Romans introduced other types and necessitated the use of several storeys which were frequently ornamented, as in the Colosseum, by attached half-columns superimposed one above the other. Therm, temples, amphitheatres, aqueducts, bridges, tombs, and basilicas all testify to the great constructive ability of the Romans, whose majestic buildings are in accord with the grandeur of Roman Imperial power.

The Romans adopted the Greek method of using large blocks of stone without mortar during the Republic, but their practical mind eventually hit upon greater economy of materials by the use of concrete, a hard composition which consists of small fragments of stone, such as tufa, peperino, marble, pumice-stone, or even broken bricks, mixed with lime. The Romans employed local slaves, liable to statute labour on public buildings, as well as the soldiers of the Roman legions—for unskilled labour under supervision sufficed—to mix the liquid concrete to the right consistency for pouring between boards to form walls (p. 135 A) or for spreading over temporary timber centering or permanent brick centering to solidify into arches and vaults (p. 135 E). This extended use of concrete originated a new constructive system which was adapted with rare sagacity to diverse types of important buildings.

Roman walls, both of stone and concrete, are of special character and must be described in detail. Walls of " opus quadratum," i.e. rectangular blocks of stone, with or without mortar joints but frequently secured with dowels or cramps, still continued in use. Concrete, both unfaced and faced, was largely employed, (a) unfaced for foundations, and (b) faced for walls, of four varieties, viz.: (i) Concrete faced with " opus incertum," i.e. irregular-shaped stones (p. 135 B). This was mainly used in the first and second centuries B.C. (ii) Concrete faced with " opus reticulatum " (p. 135 C), so-called because the joints were in diagonal lines, like the meshes of a net (reticulum). (iii) Concrete faced with " opus testaceum," i.e. with bricks (testee) triangular on plan and about 1 1/2 ins. thick (p. 135 D), used from the time of the Republic till the end of the Western Empire. (iv) Concrete faced with " opus mixtum," which consisted of bands of tufa introduced at intervals in the ordinary brick facing.

Concrete was a manufactured article, and as such was not special to any country and could be used in every part of the Empire ; thus throughout the Roman dominions it gave uniformity and similarity to the buildings, whose character was thus largely independent of local conditions.

The character of Roman architecture depended largely on the extended use of vaulting inherited from the Etruscans and standardised as a structural system. Concrete vaults were erected which were never equalled in magnitude till the introduction of steel for building in the nineteenth century. The adoption of concrete and the method of its use was far-reaching in its results, as structures of complicated plan were easily roofed by vaults of various forms, supported on centering or temporary wooden framework till the concrete had set. Sometimes such vaults were constructed, according to Choisy, of brick ribs with concrete filling (p. 135 E). The various vaults used in Roman buildings were as follows (p. 135) : (a) The semicircular or waggon-headed vault, otherwise known as the " barrel " or " tunnel " vault, was borne throughout its length on the two parallel walls of a rectangular apartment (p. 302 A). (b) The cross-vault (pp. 302 B, 303 A), which was formed by the intersection of two semi-circular vaults of equal span, was used over a square apartment and the pressure was taken by the four angles. When cross-vaults were used over long halls or corridors, the hall was divided by piers into square bays, each of which was covered with a cross-vault, which allowed of the insertion of windows in the upper part of the walls as in the tepidarium of the Thermae of Caracalla (p. 135 L) and the Therm e of Diocletian, Rome (p. 161 A). The lines of intersection of these cross-vaults are known as " groins." (c) Hemispherical domes or cupolas (cupa = a cup) (p. 154) were used over circular structures, and semi-domes for exedra or semi-circular recesses (p. 135 H, K).

In all these vaulting forms concrete was the important factor, for, owing to its cohesive power, vaults and domes of enormous size were daringly constructed, and as they were cast in one solid mass, and had the rigidity of a porcelain cup, there was little or no lateral thrust. In the Thermae of Caracalla (p. 135 L) and the Basilica of Constantine (p. 135 J) brick arches or ribs were embedded, probably as permanent centering, in the concrete vaults, especially at the " groins " as in the Thermae of Diocletian (p. 135 M), but they sometimes penetrate only a few inches into the thick concrete. With the use of concrete, decoration had little connection with construction ; for concrete was a material which required a facing, both for protection and decoration, and walls of concrete were sheathed externally and internally with marble, stone, brick, or mosaic, and these materials merely formed an appropriate finish to the structure, thus differing essentially from the homogeneous marble walls of Greek architecture. Besides many-coloured marbles, cements and stuccoes (" opus albarium ") were also frequently used for wall surfaces, and the final coat was polished. Mural paintings also were executed on prepared stucco, and were of different types, such as fresco, tempera, varnish, and caustic painting.

Marble, alabaster, porphyry, and jasper, when applied to a thick cement backing, were usually attached to the walls by iron or bronze cramps. Mosaics were used to ornament not only walls and vaults, but also floors. They are divided by Middleton into : (a) " Opus tesselatum " (" vermiculatum ") made of square tesserae of stone, marble, or many-coloured glass to form patterns or even pictures. (b) " Opus sectile " (" scutulatum ") of tesserae of marble, porphyry, or glass cut into shapes to form the pattern, and of this " opus Alexandrinum " is a very rich variety. (c) " Opus spicatum " made of paving bricks set in herring-bone pattern. Glass mosaics, sometimes forming elaborate figure pictures, were used to decorate walls and vaults, but not floors. Gilded bronze covered roofs of important buildings, such as the Pantheon (p. 149).

The abundance of statues brought from Greece led to the formation of wall niches for their reception, and these were either semicircular or rectangular, and were occasionally flanked by columns supporting a pediment, to form a frame for the statue, or were fronted by a screen of columns, as in the Pantheon (pp. 153 B, 154 B).



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