Gabinus_ or _Sperone_, a compact volcanic concrete found in the neighbourhood of the ancient Gabii on the road to Tivoli, extensively used in the construction of the earliest monuments, particularly the Tabularium and the huge Arco de Pantani. Brick was also largely employed in the construction of the foundations and inner walls of public buildings, being arranged at a later date into ornamental patterns, to which the names of _opus incertum_ and _opus reticulatum_ were given; and in the manufacture of this substance, which they were probably at first taught by the Etruscan artificers of Veii in the neighbourhood, the Romans reached a high degree of perfection. The earliest tombs along the Appian Way were constructed of these different varieties of building materials. The sarcophagi of the Scipios were hollowed out of simple blocks of peperino stone; and the sculptor's art and the material in which he wrought were worthy of the severe simplicity of the heroic age. But towards the close of the Republican period, Rome began to be distinguished for the magnificence of its public monuments. As its area of conquest spread, so did its luxury increase. New divinities were introduced from foreign countries, and domesticated in the Capitol; and these required more sumptuous fanes than those with which the native deities had been contented. The brown tufa of the Tarpeian Rock sufficed for the rude sanctuary of Vesta, the primitive hearth-stone of ancient Rome; but in the reconstruction of the sumptuous temple of Jupiter Capitolinus, which marked the grandest period of Roman history, the most precious stones of Asia and Africa were employed. Statues were imported wholesale from Greece to adorn temples and theatres, constructed after the models of Greek architecture, with pillars, friezes, and floors of precious Pentelic and Sicilian marble. During the last century of the Republic marble became a common building-stone. The tomb of Caecilia Metella, and the temples of Ceres, Juno Sospita, and Castor and Pollux, indicate the introduction of this precious and beautiful material. But it was reserved for the period of the Empire to complete the architectural glories of the city. Travertine, usually called _Lapis Tiburtinus_, a straw-coloured volcanic limestone excavated in the plain below Tivoli, which has the useful property of hardening on exposure, was now used as the principal building-stone instead of the former lavas and tufas; and the Colosseum, entirely constructed of travertine, which was treated in the middle ages as a quarry, out of which were built many of the palaces and churches of Rome, attests to this day the beauty and durability of this material. Quarries of crystalline marbles, admirably adapted for the purposes of the sculptor and architect, were opened in the range of the Apennines overlooking the beautiful Bay of Spezia, in the vicinity of Carrara, Massa, and Seravezza, and largely worked in the time of Augustus.