Rome

Unfortunately for the aesthetic qualities of Roman architec ture the process of making a cheap and durable, though ugly, con crete was discovered at about the same time. Since good sand is difficult to find near Rome, volcanic ash (pozzolana), which lies in abundance everywhere in Latium, was substituted. This ash is of course a crushed dehydrated slag, and it was eventually found that if the ash was taken from deep pits where rain-water had not destroyed its qualities it would mix with lime into a very firm hydraulic cement. By adding a filler of tufa fragments a very cheap and durable concrete could thus be made. Concrete was first used freely in the foundations and podia of the temple of Concord in 120 B.C. and the temple of Castor in 117 B.C., but it is found even earlier in a part of the platform that was constructed in front of Castor several years before. This platform probably belongs to the Gracchan period. Concrete however came into free use in superstructures only in the age of Caesar, when marble was im ported in such abundance that it could be used as a veneer for ugly concrete walls. The great importance of concrete for Roman architecture lay in the fact that during the empire, when Rome required very extensive structures, domes and vaults of immense span could be built of this material. During the empire most of the heavy walls were constructed of concrete because of its cheap ness and durability. They were usually faced with brick or with marble slabs. The bricks when used were generally triangular with one angle stuck into the concrete ; the marble slab veneering was usually held in place by iron clamps.

Though the art of making good terra-cotta ware was known in primitive Rome, and roof-tiles of terra-cotta of excellent quality had freely been used for six centuries before Augustus' day, bricks were not burned at Rome for use in wall-construction during the republic. Immense heaps of fragments of broken roof-tiles had however accumulated, and the Augustan architects began to use these fragments in facing concrete walls. When this supply gave out, triangular bricks were made for the same purpose—dur ing the reign of Claudius—and when, after the great fire of Nero's day, a vast programme of rebuilding followed, brick yards turned out an immense quantity of material for the facing of concrete walls. This material continued to be used freely through imperial times.

Marble was very expensive and relatively few buildings were made of solid marble ; but for veneering, for columns, entablatures and decorative members large quantities of marble were imported. A few wealthy nobles had imported marble columns for their porti coes before Caesar's day. While Caesar was governor of Cisalpine Gaul his architects and engineers began to import to Rome Car rara marble, found in that province. The architects of Augustus developed the Numidian quarries of Simitthu, which yielded a variety of yellow and cream colotired marbles of great beauty (giallo antico). The transportation costs were very heavy since it had to be brought loom. over land before it was loaded on ships. Its use was largely confined to decorative purposes. The pavonaz zetto of Synnada, zoom. inland from Smyrna in Asia Minor, also came into use, as well as the greenish cipollino of Euboea, the mar bles of Pentelicon, Hymettus and Paros, and the red granites of Aswan in Egypt. During the empire architects vied with each

other in attaining new colour effects with contrasting veneers, and the Christian basilicas and churches of Rome which are decorated with the marbles stripped from Roman buildings are rich with stones that the emperors had imported from all parts of the world. Besides those mentioned we may name the products of quarries of Chios (called Africano), Thasos (porta santa), Laconia (rosso antico and nero antico), Thessaly (verde antico), and the alabas ters and porphyries of Egypt.

Early Town Walls.

Tradition speaks of very early fortifica tions around the Palatine and Capitoline hills. These may have been earthen mounds bearing a fence of stakes. There is no doubt that a stone wall was constructed of cappellaccio blocks around the whole city at the time of the Etruscan kings. This wall was almost wholly rebuilt after the Gallic fire (387 B.c.) with the stronger Grotta Oscura stone, and later strengthened and improved from time to time with better materials. This so-called Servian wall (at first not including the Aventine) was nearly 6km. long. It began at the Tiber near the present Ponte Rotto, had two gates between the Tiber and the Capitoline hill, skirted the Capitoline on its west side (where a few blocks of the 4th-century wall are visible), then proceeded across the valley to the edge of the Quirinal hill. A small gate (perhaps an embrasure for artillery) is still visible inside the Palazzo Antonielli, but this consists of Anio tufa and must date from about the time of the first civil war. The fragment of wall seen in the via Nazionale just above is of Grotta Oscura stone belonging to the 4th century. From this point the wall fol lowed the edge of the Quirinal hill north-eastwards for over a mile to the porta Collina. At the via Finanze may be seen a well pre served portion in cappellaccio. Because of the material this part has usually been assigned to the 6th century, but the fine work manship and battering would rather indicate a 4th century recon struction. From the Porta Collina the wall turned southwards across the level plateau to the porta Esquilina, a distance of about a mile. Here the city was especially exposed to attack and the wall was not only made with special care in the 4th century but was later frequently strengthened and repaired. In constructing this portion a moat 3oft. deep and iooft. wide was dug and the earth of this excavation was used for an agger about 4oft. thick. The stone wall itself that stood behind the moat and supported the mound was about 'oft. thick and more than 3oft. high and was made of Grotta Oscura stone. The inner side of the agger was sup ported by a lower cappellaccio wall. The numerous quarry marks found in the section near the railway station are probably those of the Etruscan workmen of the 4th century, while those found at Piazza Fanti seem to belong to the repairs of the second Punic War. The Gabine and Monte Verde stones of the reconstructed Viminal gate may belong to the time of the Social War, while the concrete work and Anio stone at Piazza Macao seem to be a part of the repairs made during the Catilinarian Rebellion or the civil war.