Of the breccias there is a great variety among the relics of ancient Rome. A breccia is a rock made up of angular pebbles or fragments of other rocks. When the pebbles are rounded the conglomerate is a pudding-stone. Marble breccias are formed of angular pieces of highly crystalline limestone, united together by a siliceo-calcareous cement, containing usually an admixture of a hornblendic substance, and which is due to a particular action of adjacent masses or veins of iron ore. The hornblendic cement, with its iron or manganese base, produces the variegated appearance which may be seen in specimens from different localities. As may be imagined from their composition, these rocks are as a rule extremely unalterable by ordinary atmospheric agencies, and are susceptible of a high degree of polish, which they retain with the utmost tenacity. They were favourite materials with the ancient Roman decorators; but they do not occur in large masses in the city. A beautiful pair of Roman Ionic columns under the pediment of the altar of the third chapel in the Church of Ara Coeli are made of a valuable breccia called Breccia dorata, distinguished by its small light-golden fragments on a ground of various shades of purple. The high altar of Santa Prisca on the Aventine is supported by one column of Breccia corallina of remarkably fine quality, in which the fragments are white on a ground of light coral-red. In the second chapel of St. Andrea della Valle there are two Corinthian columns of Breccia gialla e nera, which is an aggregate mass of yellow and black fragments: the yellow in its brilliant golden hue surpassing that of all other marbles, and forming a striking contrast to the long irregular black fragments interspersed throughout it. In the first chapel of the same church there are four fluted Corinthian columns of breccia gialla, containing small and regular blotches, of which the prevailing tint is orange, each fragment edged with a rim of deeper yellow that surrounds it like a shadow. A most beautiful variety of Breccia gialla e nera forms the basin of holy water at the entrance of the Church of St. Carlo di Catinari, in which "the colours resemble a golden network spread upon a ground of black"; and an exceedingly lovely urn is seen underneath the altar in one of the chapels of the Portuguese Church, in which white fragments are imbedded in a purple ground which shines through their soft transparency.
Not the least attractive objects in the chamber of the Dying Gladiator in the Museum of the Capitol area portion of a large column of very beautiful and extremely valuable Breccia tracagnina, in which golden-yellow, white, red, and blue fragments occur in very nearly equal proportions, and two large pedestals of Breccia di Sete-Bassi—so called from the discovery of the first specimens near the ruins of the Villa of Septimus Bassus on the Appian Way—containing very small purple fragments of an oblong shape, which is the characteristic peculiarity of all the varieties of this species of marble. Probably the most beautiful of all the ancient breccias is that called Breccia della Villa Adriana, from its occasional occurrence in the ruins of Hadrian's Villa, and also Breccia Quintilina, from its having been found in the grounds of the magnificent Villa of Quintilius Varus, commemorated by Horace, at Tivoli, now occupied by the Church of the Madonna di Quintigliolo. The prevailing colour of the fragments is that of a dark brown intermixed with others of smaller size, of red, green, blue, white, purple, bright yellow, and sometimes black, all harmonising together most beautifully. The comparatively small pieces found at Tivoli now adorn the Churches of St. Andrea della Valle, famous for its rich varieties of breccias, St. Domenico e Sisto and Santa Pudenziana, where they appear among the marble sheathing of the walls. In the chapel of the Gaetani in the last-mentioned church, the wall is incrusted with the richest marbles, especially Lumachella and Brocatello, and large tablets of Hadrian's breccia setting off the splendid sarcophagus of Breccia nera e gialla dedicated to Cardinal Gaetani.
Along with the breccias which I have thus incidentally noticed, but to which a whole essay might be devoted on account of their beauty, rich variety, and great value and rarity, should be classified a kind of "breccia dure," called Breccia d' Egitto. It is not, however, a true breccia, but a pudding-stone, composed, not of calcareous but of siliceous fragments; and these fragments are not angular, as in the true breccias, but rounded, indicating that they had been carried by water and consequently rounded by attrition. The connected pebbles must have been broken from rocks of great hardness to have withstood the effects of constant abrasion. In the Egyptian breccia are found very fine pebbles of red granite, porphyry of a darker or lighter green, and yellow quartz, held together by a cement of compact felspar. It has a special geological interest, inasmuch as it represents an ancient sea-beach flanking the crystalline rocks of Upper Egypt, where the cretaceous and nummulitic limestones end. The pebbles were derived from the central nucleus of granite from beyond Assouan to the upper end of the Red Sea, round which are folded successive zones of gneiss and schist pierced by intrusive masses of porphyry and serpentine. The pair of beautiful Grecian Ionic columns, and the large green tazza—eighteen feet in circumference—the finest specimen of Egyptian breccia to be seen in Rome, both in the Villa Albani, and the vase of the same material in the chamber of Candelabra in the Vatican, in which the prevailing green colour is crossed by several stripes of pure white quartz, may thus have been sculptured out of a portion of littoral deposit formed from the ruins of the crystalline rocks of the mountain group of Sinai. There is something extremely interesting and suggestive to the imagination in the twofold origin of these conglomerate ornaments of the palaces of Rome. Around them gather the wonderful associations of ancient human history, and the still more awe-inspiring associations of geological history. They speak to us of the conquests of Rome in the desolate tracts of Nubia and Arabia, from which the spoils that enriched its palaces and temples were derived; and of the existence of coast-lines, when Egypt was a gulf stretching from the Mediterranean to the Mountains of the Moon, which became silted up by slow accumulations. Their language, in both relations, is that of ruin. They are survivors both of the ruins of Nature and of Man, and are made up of the wrecks of both. Older far than the marbles which keep them company in the sculptor's halls and churches of Rome, and whose human history is equally eventful, their materials were deposited along the shore of a vanished sea, when the mountains that yielded these marbles lay as calcareous mud in its depths.
Alabasters, of which there are numerous varieties, from pure diaphanous white to the deepest black, were favourite decorative materials with the ancient Romans. The different kinds were used for the walls of baths, vases, busts, pillars, and sepulchral lamps, in which the light shining through the transparent sides had an agreeable softness. Cornelius Nepos, as quoted by Pliny, speaks of having seen columns of alabaster thirty-two feet in length; and Pliny says that he himself had seen thirty huge pillars in the dining-hall of Callistus, the freedman of Claudius. One such column still exists in the Villa Albani, which is twenty-two and a half feet in height. The ancients obtained large blocks of alabaster from quarries in Thebes in Egypt, in the neighbourhood of Damascus, and on Mount Taurus. They imported some kinds also from Cyprus, Spain, and Northern Africa. They obtained varieties nearer home, in different parts of Italy, such as the beautiful Alabastro di Tivoli, employed by Hadrian in his villa, and which appears to have been brought from Terni, where it still exists in abundance. From the quarry near Volterra the Etruscans obtained the alabaster for their cinerary urns. The European alabasters are accumulated masses of stalactite and stalagmite, formed by the slow dropping of water charged with sulphate of lime, to which circumstance they owe the parallel stripes or concentric circles with which they are marked, while the rich and delicate varieties of colouring are produced by the oxides of iron which the water carries with it in its infiltration through the intervening strata. They are very soft and perishable, and consequently are very rarely found among the ruins of ancient Rome. The Oriental alabasters, on the other hand, which are distinguished from the European by their superior hardness and durability, are in reality not sulphates, but carbonates of lime. Their hardness is quite equal to that of the best statuary marbles. The ancient quarries on the hill—the modern Mount St. Anthony—near the town of Alabastron, in Middle Egypt, from which the material got its name, have only recently been re-opened, but blocks of large size and perfect beauty have been obtained. Owing to the facility with which alabaster can be reduced by fire to lime, very few large examples of it in Rome have escaped the ruthless kilns of the middle ages. The most interesting specimens of ancient alabaster are the very beautiful vase of Alabastro cotognino, prolate in form, and in colour white, streaked with very light pink, which contained the ashes of Augustus, found in the ruins of his mausoleum, and now in the Vatican; the bust of Julius Cæsar, made of the variety tartaruga, from the resemblance of its brownish-yellow markings to tortoise-shell, in the Museum of the Capitol; and the two large blocks of alabastro a pecorella, brought from the Villa of Hadrian, in the fourth portico of the Vatican, the largest and most beautiful specimens of this very rare alabaster in Rome, distinguished by white circular blotches, like a flock of sheep huddled together, on a deep blood-red ground. In the churches there are numerous specimens of all the varieties, forming the columns and sheathings of altars, memorial chapels, and monuments; the incrustations of alabaster on the walls of the Borghese chapel, in Santa Maria Maggiore, being conspicuous for their splendid effect. The baldacchino above the high altar of St. Paul's is supported by four splendid columns of Oriental alabaster presented to Gregory XVI. by Mehemet Ali, the viceroy of Egypt. An interesting collection of beautiful and valuable varieties of alabasters may be made in connection with the building operations still carried on in the unfinished façade of the basilica fronting the Tiber.
The well-known Verde antico is not a marble, but a mixture of the green precious serpentine of mineralogists and white granular limestone. It may also be called a breccia, for it is composed of black fragments, larger or smaller, derived from other rocks, whose angular shape indicates that they have not travelled far from the spots where they occur. The ancient Romans called it Lapis Atracius, from Atrax, a town in Thessaly, in the vicinity of which it was found. It can hardly be distinguished, except by experts, from the modern green marbles of Vasallo in Sardinia, and Luca in Piedmont. It occurs somewhat abundantly in Rome, having been a favourite material with the old Romans for sheathing walls and tables. Magnificent columns of it were introduced into the temples and triumphal arches. We find relics of these in the older churches. Four splendid fluted Corinthian columns of Verde antico, with gilded capitals, support the pediment of the high altar in Sta. Agnese, in the Piazza Navone, which formerly belonged to the Arch of Marcus Aurelius in the Corso. A pair of very fine columns of this precious stone flank each of the niches, containing statues of the twelve apostles, in the piers which divide the middle nave from the side ones in the Church of St. John Lateran. These twenty-four columns are remarkable for the clearness of the white, green, and black colours that occur in them. They are supposed to have been taken from the Baths of Diocletian. Two of the splendid composite columns which support the pediment of the altar in the Corsini chapel of this church are of this marble, and were also taken from the Arch of Marcus Aurelius in the Corso. One most magnificent column of Verde antico has been found, along with seven others of different marbles, in the wall of the narthex of the subterranean Church of San Clemente. A small portion of it is polished to show the beauty of the material, while the rest is dimmed and incrusted with the grime of age.
Very different from this is the ancient serpentine or ophite of Sparta called the Lapis Lacedæmonius, found in different hills near Krokee, or in Mount Taygetus in Lacedæmon, where the old quarry has recently been opened. It has a base of dark green with angular crystals of felspar of a lighter green imbedded in it. It is a truly eruptive rock, occurring in intrusive bosses, or in beds interstratified with gneiss and mica-schist, and owes its various shades of green to the presence of copper. Owing to its extraordinary hardness, this stone was seldom used for architectural purposes; and the lapidary will charge three times as much for working a fragment of this material into a letter-weight as for making it of any other stone. A pair of fluted Roman Ionic columns, supporting the pediment of the altar of the chapel of St. John the Baptist, in the Baptistery of St. John Lateran, are the only examples of ophite pillars in Rome. Next to these the largest masses are a circular tablet, forming part of the splendid sheathing of one of the ambones in the Church of San Lorenzo; and two elliptical tablets, still larger, engrafted upon the pilasters in front of the high altar of St. Paul's.
The principal use to which this stone was devoted in Rome was the construction of mosaic pavements. The emperor Alexander Severus introduced into his palaces and public buildings a kind of flooring composed of small squares of green serpentine and red porphyry, wrought into elegant patterns, which became very fashionable, and was called after himself Opus Alexandrinum. The infamous Heliogabalus had previously paved some of the courts of the Palatine with such intarsio work, but his cousin Alexander Severus, following his example, adorned with it all the terraces and walks around, and the pavements within, the isolated villas called Diætæ, dedicated to his mother Mammæa, which he added to the Palatine buildings. We have examples of this beautiful kind of tesselated pavement in some of the chambers of the Baths of Caracalla; and it is highly probable that the Opus Alexandrinum in the transept and middle nave of the Church of Santa Maria in Trastevere is in part at least contemporaneous with Alexander Severus, who conceded the ground on which the original oratory stood to Pope Calixtus I. in 222, for the special use of the Christians. If this be so, we have in this first place of Christian worship established in Rome the first instance of the application of Opus Alexandrinum to the decoration of a church. In the middle ages the fashion was beautifully imitated by artists of the Cosmati family and their school; and the mosaic pavements of this kind in the medieval churches of Rome are no older than this period. But we have reason to believe that the Opus Alexandrinum in two of the chapels of Santa Maria degli Angeli was taken from the Baths of Diocletian; while the splendid pavement of the whole church, naves, transept, and choir of Santa Croce in Jerusalemme, formed originally part of the decorations of the Sessorian Palace of Sextus Varius, the father of Heliogabalus, after whom the church is sometimes called the Sessorian Basilica. The flooring of the whole upper church of San Clemente was transferred from the older subterranean church, which derived its pavement from some of the ruins of the Palatine or the Forum; and the serpentine fragments, which enter very largely into the composition of the curious old mosaic floor of Ara Coeli must have had a similar origin as far back as the time of its founder, Gregory the Great. The Lapis Lacedæmonius must have been very abundant in Rome during the time of Alexander Severus—judging from the quantities that are made up into mosaics in the churches, and the heaps of broken fragments that are found on the Palatine and at the Marmorata. The circular space around the obelisk in the Piazza of St. Peter's to a considerable extent is paved with it; and specimens of it frequently occur among the ordinary road-metal in the city and neighbourhood.
Sicilian jaspers, so called, though really marbles, and purely calcareous, because of their resemblance in colour and form of the blotches to jasper, were wrought in great variety in the quarries in the neighbourhood of the celebrated Taormina, and were transported in the form of columns to Rome. Siliceous jaspers, obtained from the crystalline rocks of Asia Minor, Egypt, and Northern Italy, were also used for columns; and their brilliant red, green, and yellow hues, highly polished, contrasted beautifully with the white marbles of the interiors of the palaces. An even more sumptuous material called Murrha was employed, which has been identified with fluor-spar, a translucent crystalline stone marked with blue, red, and purple, similar to the beautiful substance found near Matlock in Derbyshire. Of this fluor-spar were formed the celebrated murrhine cups which were in use in Rome in the days of Pliny among the richest people, and for which fabulous prices were paid. Several blocks of this material were found some years ago at the Marmorata which had been originally imported from Parthia in the reign of Hadrian. One of them was employed by the Jesuits, when cut up into thin slices, in ornamenting the principal altar in the church of Il Gesu. One of the chambers in the Baths of Titus was paved with slabs of the finest lapis lazula—the Lapis Cyanus of the ancients—derived from the spoils of the Golden House of Nero, and originally procured by order of the luxurious tyrant from Persia and the neighbourhood of Lake Baikal. We can trace fragments of this exquisite pavement in the decoration of the chapel of St. Ignatius in the Church of the Jesuits. The globe, three feet in diameter, over the altar, beneath which repose the remains of Ignatius Loyola, is sheathed with this most precious stone, whose brilliant blue, contrasting with the white marble of the group of the Trinity—one of whose members holds it in His hands—has a splendid effect. The rare and costly marbles with which the Church of Il Gesu is profusely adorned were mostly taken from the ruins of the Baths of Titus by Cardinal Farnese in 1568. From the same source came also the magnificent sarcophagus, sheathed with lapis lazula, under the altar of St. Ignazio, which holds the body of St. Luigi Gonzaga.
But it is impossible, within the limits of this chapter, to describe fully the relics of other precious and beautiful stones which may be found among the ruins of ancient Rome, or among the churches to which they have been transferred. Profuse as were the ancient Romans in their general expenditure, upon no objects did they lavish their wealth so extravagantly as upon their favourite marbles and precious stones for the decoration of their public buildings and their private houses. No effort was spared that Rome might be adorned with the richest treasures of the mineral kingdom from all parts of the world. Slaves and criminals were made to minister to this luxury in the various quarries of the Roman dominions, which were the penal settlements of antiquity. The antiquary Ficoroni counted the columns in Rome in the year 1700, and he found no less than eight thousand existing entire; and yet these were but a very small proportion of the number that must once have been there. The palaces and modern churches of Rome owe, as I have said, all their ornaments to this passion of the ancients. There is not a doorstep nor a guardstone at the corner of the meanest court in Rome which is not of marble, granite, or porphyry from some ancient building. Almost all the houses, as Raphael said, have been built with lime made of the costly old marbles. The very streets in the newly-formed parts of the city are macadamised with the fragments of costly baths and pillars. I took up one day, out of curiosity, some of the road-metal near the Church of Santa Maria Maggiore, and I identified in the handful no less than a dozen varieties of the most beautiful marbles and porphyries from Greece, Africa, and Asia. And when we remember that all these foreign stones were brought into Rome during the interval between the end of the Republic and the time of Constantine—a period of between three hundred and four hundred years—we can form some idea of the extraordinary wealth and luxury of the Imperial City when it was in its prime.