stratified form, with frequent cavities and fissures lined with crystals. As Vitruvius (ii. 5) says, it is a good weather-stone, but is soon calcined by fire. If laid horizontally it is very strong, but if set on end its crystalline structure is a great source of weakness, and it splits from end to end. Neglect on the part of Roman builders of this important precaution in many cases caused a complete failure in the structure. This was notably the case in the rostra. (6) Pulvis Puteolanus (pozzolana), so called from extensive beds of it at Puteoli—a volcanic product, which looks like red sandy earth, and lies in enormous beds under and round the city of Rome. When mixed with lime it forms a very strong hydraulic cement, of equal use in concrete, mortar or undercoats of stucco. It is to this material that the concrete walls of Rome owe their enormous strength and durability, in many cases far exceeding those of the most massive stone masonry. Vitruvius devotes a chapter (bk. ii. ch. 6) to this very important material.
Bricks were either sun=dried (lateres crudi) or kiln-baked (lateres cocti, testae). The remarks of Vitruvius (ii. 3) seem to refer wholly to sun-dried bricks, of which no examples now exist in Rome. It is important to recognize the fact that among the existing ancient buildings of Rome there is no such thing as a brick wall or a brick arch in the true sense of the word; bricks were merely used as a facing to concrete walls and arches and have no constructional importance.[1] Concrete (opus caementicium, Vitr. ii. 4, 6, 8), the most important of all the materials used, is made of rough pieces of stone, or of fragments of marble, brick, &c., averaging from about the size of a man's fist and embedded in cement made of lime and pozzolana-forming one solid mass of enormous strength and coherence. Stucco, cement and mortar (tectorium, opus albarium and other names) are of many kinds; the ancient Romans especially excelled in their manufacture. The cement used for lining the channels of aqueducts (opus signinum) was made of lime mixed with pounded brick or potsherds and pozzolana; the same mixture was used for doors under the “nucleus” or finer cement on which the mosaic or marble paving-slabs were bedded, and was called caementum ex testis tunsis. For walls, three, or four coats of stucco were used, often as much as 5 in. thick altogether; the lower coats were of lime and pozzolana, the finishing coats of powdered white marble (opus albarium) suitable to receive painting. Even marble buildings were usually coated with a thin layer of this fine white stucco, nearly as hard and durable as the marble itself—a practice also employed in the finest buildings of the Greeks—probably because it formed a more absorbent ground for coloured decoration; stone columns coated in this way were called “columnae dealbatae” (Cic. In Verr. ii. 1, 52 seq.). For the kinds of sand used in mortar and stucco, Vitruvius (ii. 4) mentions sea, pit and river sand, saying that pit sand is to be preferred.
Marble appears to have come into use about the beginning of the 1st century B.C. Its introduction was at first viewed with great Decorative materials. jealousy, as savouring of Greek luxury. The orator Crassus was the first to use it in his house on the Palatine, materials built about 92 B.C.; and, though he had only six small columns of Hymettian marble, he was for this luxury nicknamed the “Palatine Venus” by the stern republican M. Brutus (Plin. H.N. xxxvi. 7). The temporary wooden theatre of the aedile M. Aemilius Scaurus, built in 58 B.C., appears to have been the first building in which marble was more largely used; its 360 columns and the lower order of its scena were of Greek marble (see Plin. H.N. xxxvi. 5, 50). In a very few years, under the rule of Augustus, marble became very common.[2]
Of white statuary marble four principal varieties were used. (1) Marmor Lunense, from Luna, near the modern Carrara (Strabo, v. p. 222), is of many qualities, from the purest creamy white and the finest grain to the coarser sorts disfigured with bluish grey streaks. (Ex., the eleven Corinthian columns-in the Borsa.) (2) Marmor Hymettium, from Mount Hymettus, near Athens, is coarser in grain than the best Luna marble and is usually marked with grey or blue striations (Strabo ix. p. 399). (Ex., the forty-two columns in the nave of S. Maria Maggiore and the columns in S. Pietro in Vincoli.) (3) Marmor Pentelicum, from Mount Pentelicus, also near Athens, is very fine in grain and of a pure white; it was more used for architectural purposes than for statues, though some sculptors preferred it above all others, especially Pheidias and Praxiteles. (Ex., the bust of the young Augustus in the Vatican.) (4) Marmor Parium, from the Isle of Paros, is very beautiful, though coarse in texture, having a very crystalline structure. (Ex., the nineteen columns of the round temple in the Forum Boarium.)
Nine chief varieties of coloured marbles were used in Rome. (1) Marmor Numidicum (mod. giallo antico; Plin. H.N. v. 22), Coloured marbles. from Numidia and Libya, hence also called Libycum, is of a rich yellow, deepening to orange and even pink. Enormous quantities of it were used, especially for columns, wall-linings and pavements. (Ex., seven columns on the arch of Constantine, taken from the arch of Trajan; the eighth column is in the Lateran basilica.) (2) Marmor Carystium (mod. cipollino), from Carystus in Euboea (Strabo x. p. 446), has alternate wavy strata of white and pale green—the “undosa Carystos” of Statius (Silv. i. 5, 34). From its well-defined layers like an onion (cipolla) is derived its modern name. (Ex., columns of temple of Antoninus and Faustina.) (3) Marmor Phrygium or Synnadicum (mod. pavonazzetto), from Synnada in Phrygia (Strabo xii. p. 577; Juv. xiv. 307; Tibull. iii. 3, 13), is a slightly translucent marble, with rich purple markings, violet verging on red. It was fabled to be stained with the blood of Atys (Stat. Silv. i. 5, 37). (Ex., twelve fluted columns in S. Lorenzo fuori le Mura, and four columns in the apse of S. Paolo fuori, saved from the ancient nave of the basilica, burnt in 1823.) (4) Marmor Iasium (probably the modern porta santa), from Iasus, is mottled with large patches of dull red, olive green and white. The “holy doors” of the four great basilicas are framed with it, hence its modern name. (Ex., the slabs in front of the hemicycle of the Rostra and four columns in S. Agnese fuori le Mura). (5) Marmor Chium (probably the modern Africano), from Chios, is similar in the variety of its markings to the portasanta, but more brilliant in tint. (Ex., a great part of the paving of the Basilica Julia and two large columns in the centre of the façade of St Peter's.) (6) Marmor Taenarium (mod. rosso antico), from Taenarum in Laconia (Strabo viii. p. 367; Pliny, H.N. xxxvi. 158), is a very close-grained marble, of a rich deep red, like blood. As a rule it does not occur in large pieces, but was much used for small cornices and other mouldings in interiors of buildings. Its quarries in Greece are still worked. (The largest pieces known are the fourteen steps to the high altar of S. Prassede and two columns nearly 12 ft. high in the Rospigliosi Casino dell' Aurora.) (7) The name Mormor Taenarium is also applied by the ancients to a black marble (nero antico) now no longer quarried. It is mentioned by Tibullus (iii. 3, 14) in conjunction with Phrygian and Carystian marbles; see also Prop. iii. 2, 9, and Plin. H.N. xxxvi. 135., (Ex., two columns in the choir of S. Giovanni in Laterano.) (8) Lapis Atracius (verde antico), found at Atrax in Thessaly, was one of the favourite materials for decorative architecture; it is not strictly a marble (i.e. a calcareous stone) but a variety of “precious serpentine,” with patches of white and brown on a brilliant green ground. It seldom occurs in large masses. (The finest known specimens are the twenty-four columns beside the niches in the nave of the Lateran basilica.) (9) The hard oriental alabaster, the “onyx” or “alabastrites” of Pliny (H.N. xxxvi. 59, xxxvii. 109); its chief quarries were on the Nile, near Thebes,[3] in Arabia and near Damascus. In Pliny's age it was a great rarity; but in later times it was introduced in large quantities, and fragments of a great many columns have been found on the Palatine, in the baths of Caracalla and elsewhere. It is semi-transparent and beautifully marked with concentric nodules and wavy strata. An immense number of other less common marbles have been found, including many varieties of breccia, whose ancient names are unknowns.[4]
From the latter part of the 1st century B.C. hard stones—granites and basalts—were introduced in great quantities. The Granites and basalts. basalts—“basanites” of Pliny (xxxvi. 58)—are very refractory, and can only be worked by the help of emery or diamond dust. The former was obtained largely at Naxos; diamond-dust drills are mentioned by Pliny (H.N. xxxvii. 200). The basalts are black, green and brown, and are usually free from spots or markings; examples of all three exist, but are comparatively rare. The red variety called “porphyry” was used
in enormous quantities. It is the “porphyrites” of Pliny (H.N.- ↑ In less solid constructions than those which have survived until modern times bricks were doubtless used by themselves.
- ↑ The oft-quoted boast of Augustus (Suet. Aug. 29) that he “found Rome of brick and left it of marble” has probably much truth in it, if for “brick” we read “peperino and tufa.” In the time of Augustus burnt brick was very little used, the usual wall facings being opus quadratum of tufa or peperino, and opus reticulatum of tufa only.
- ↑ These Nile quarries were worked during the 19th century, and many blocks were imported into Rome for the rebuilding of S. Paolo fuori le Mura.
- ↑ On the subject of Roman marbles, see Corsi, Delle pietre antiche (ed. 3, 1845). and Pullen, Handbook of Roman Marbles (London, 1894); also Brindley in Transactions of the Royal Institute of British Architects (1887). A collection of 1000 specimens, originally formed by Corsi, is preserved in the museum at Oxford.
