The quarries of the third quality were, or rather one of them was, discovered on February 7, 1872, in the Vigna Querini, outside the Porta St. Lorenzo, near the first milestone of the Vicolo di Valle Cupa. It was a surface quarry, comprising five trenches 16 feet wide, 9 feet deep. Some of the blocks, already squared, were lying on the floor of the trenches, others were detached on two or three sides only, the size of others was simply traced on the rock by vertical or horizontal lines. This tufa, better known by the name of cappellaccio, is very bad. The only buildings in which it was used, besides the inner wall of the Servian agger, are the platform of the temple of Jupiter Capitolinus, in the gardens of the German Embassy, and the "puticuli" in the burial-grounds of the Esquiline. Its use must have been given up before the end of the period of the Kings, in consequence of the discovery of better quarries on the right bank of the Tiber, at the foot of the hills now called Monte Verde....
They cover a space one mile in length and a quarter of a mile wide on each side of the valley of Pozzo Pantaléo. In fact, this valley, which runs from the Via Portuensis toward the lake of the Villa Pamphili, seems to be artificial; I mean, produced by the extraction of the rock of millions of cubic meters in the course of twenty-four centuries. If the work of the ancient quarrymen could be freed from the loose material which conceals it from view, we should possess within a few minutes' drive from the Porta Portese a reproduction of the famous mines of El Masarah, with beds of rock cut into steps and terraces, with roads and lanes, shafts, inclines, underground passages, and outlets for the discharge of rain-water. When a quarry had given out, its galleries were filled up with the refuse of the neighboring ones—chips left over after the squaring of the blocks; so that, in many cases, the color and texture of the chips do not correspond with those of the quarry in which they are found. This layer of refuse, transformed by time into humus, and worked upon by human and atmospheric forces, has given the valley a different aspect, so that it looks as if it were the work not of quarrymen, but of nature.
Tufa may be found used in many existing monuments of ancient Rome, such as the drains of the middle and southern basin of the left bank, the channels and arches of the Marcia and Anio Vetus, the Servian walls, the temples of Fortuna Virilis, of Hercules Magnus Custos, the Rostra, the embankment of the Tiber, etc. The largest and most magnificent quarries in the suburban district are the so-called Grotte della Cervara. No words can convey an idea of their size and of the regularity of their plan. They seem to be the work of a fanciful architect who has hewn out of the rock halls and galleries, courts and vestibules, and imitated the forms of an Assyrian palace.
For the study of the peperino mines, which contain a stone special to the Alban district, formed by the action of hot water on gray volcanic cinders, the reader should follow on foot the line of the new Albano railway, from the place called Il Sassone to the town of Marino. Many of the valleys in this district, now made beautiful by vineyards and oliveyards, owe their existence to the pickax of the Roman stonecutter, like the valley of Pozzo Pantaléo. The most curious sight is a dolmen or isolated rock 10 meters high, left in the center of one of the quarries to certify the thickness of the bed of rock excavated. In fact, the whole district is very interesting both to the archeologist and to the paysagiste. The mines of Marino, still worked in the neighborhood of the railway station, would count, like the Grotte della Cervara, among the wonders of the Campagna, were they known to the student as they deserve to be.
The principal Roman buildings in which the lapis Albanus has been used are: the Claudian aqueduct, the Cloaca Maxima, the temples of Antonius and Faustina, of Cybele, of the Eventus Bonus, of Neptune, the inclosure wall of the Forum Augustum, Forum Transitorium, and Forum Pacis, the Porticus Argonautarum, Porticus Pompeii, the Ustrinum of the Appian Way, etc. The sarcophagus of Cornelius Scipio Barbatus in the Vatican museum, and the tomb of the Tibicines in the Museo Municipale al Celio are also of this stone.
Travertine stone was quarried in the plains of Tivoli at places now called Le Caprine, Casal Bernini, and Il Barco. This last was reopened after an interval of many centuries by Count G. Brazza, brother of the African explorer. Lost in the wilderness and overgrown with shrubs, it had not been examined, I believe, since the visit of Brocchi. It can be reached by stopping at the station of the Aquae Albulae, on the Tivoli line, and following the ancient road which led to the works. This road, twice as wide as the Appian Way, is flanked by substructures, and is not paved, but macadamized. Parallel with it runs an aqueduct which supplied the works with motive power, derived probably from the sulfur springs. There are also remains of tombs, one of which, octagonal in shape, serves as a foundation to the farmhouse del Barco.
The most remarkable monument of the whole group is the Roman quarry from which five and a half million cubic meters of travertine have been extracted, as proved by the measurement of the hollow space between the two opposite vertical sides. That this is the most important ancient quarry of travertine, and the largest one used by the Romans, is proved, in the first place, by its immense size. The sides show a frontage of more than two and a half kilometers; the surface amounts to 500,000 square meters. The sides are quite perpendicular, and have the peculiarity of projecting buttresses, at an angle of 90 degrees. Some of these buttresses are isolated on three sides, and still preserve the grooves, by means of which they could be separated from the solid mass....
In order to keep the bottom of the works clean and free from the movement of the carts, for the action of the cranes, and for the maneuvres of the workmen, the chips, or useless product of the squaring of the blocks, were transported to a great distance, as far as the banks of the Anio, and there piled up to a great height. This is the origin of that chain of hills which runs parallel to the river, and of whose artificial formation no one, as far as I know, had the least suspicion. One of these hills, visible from every point of the neighboring district, from Hadrian's villa as well as from the Sulfur Baths, is elliptical in shape, 22 meters high, 90 meters long, and 65 meters wide. It can with reason be compared with our Testaccio. It is easy to imagine how immense must have been the number of blocks cut from the Cava del Barco during the period of the formation of this hill alone. Another proof of the antiquity of the quarry, and of its abandonment from imperial times down to our own day, is given by this fact....
There are three collections of brick-stamps in Rome; one, of little value, in the Kircherian museum; the second in the last room of the Vatican library, past the "Nozze aldobrandine;" the third and best in the Museo Municipale al Celio. This last contains over a thousand specimens, and a unique set of the products of Roman kilns. In fact, the first hall of the Museo is set apart exclusively for the study of ancient building and decorative materials.
Roman bricks were square, oblong, triangular, or round, the latter being used only to build columns in the Pompeiian style. The largest bricks that have been discovered in my time measure 1.05 meters in length. They were set into an arch of one of the great stairs leading to the avenue or boulevard established in Imperial times on the top of the agger of Servius. Roman bricks are very often stamped with a seal, the legend of which contains the names of the owner and the manager of the kilns, of the maker of the tile, of the merchant entrusted with the sale of the products, and of the consuls under whose term of office the bricks were made. These indications are not necessarily found all in one seal.