referred satisfactorily to the respective periods of their erection; thus the walls formed of large square blocks of stone, not sawn, but wrought into shape with a hammer, or some such tool, and fixed without mortar, are referred to the time of the kings. So, again, the walls of small stones, arranged lozenge-wise (composed of tufa), are of the republican period; whilst those of tufa, with horizontal layers of tiles, are of the latest period of the republic; the Imperial work being entirely of brick, the bricks very thin, some at least two feet long, and beautifully arranged.

There were several varieties of stone employed by the Romans in their buildings:-1. Tufa, a volcanic sandstone, called by Vitruvius, Lapis ruber, Tophus. The ancient quarries of this are in the Cælian, Aventine, and Capitoline hills. The walls of Romulus are entirely of this material, and were probably built from quarries in the Palatine hill itself. 2. Lapis Albanus, now called Peperino, also a volcanic sandstone, but hard and rough, the surface covered with knobs of flint. The ancient quarries are near Alba Longa, on Monte Cavo. The Mamertine Prison, the Agger of Servius Tullius, and the Temple of Antoninus and Faustina, are of this material. 3. Lapis Gabinus, called Sperone. This resembles the Peperino, but it is not easy to distinguish them. The ancient quarries are at Gabii. The triple arch of the Cloaca Maxima, and the substructure of the Tabularium, are of this material. 4. Lapis Tiburtinus, called Travertino, or Travertine, a limestone; the ancient quarries of which are at Tibur, or Tivoli, near the Anio. It is white when new and becomes a warm yellow. The tomb of Cecilia Metella and the Colosseum are well known examples of this stone.

The earliest kind of construction in stone is the opus quadratum. The stones are squared, but not necessarily square; they are usually oblong, and in the earliest examples these large stones are laid alternately lengthwise and crosswise, like modern bricks. This kind of construction has been divided into several periods by Mr. Parker. The earliest and best example is the wall of Romulus on the Palatine, which is decidedly of Etruscan character. In Rome the only material for these walls is tufa. The stones of this earliest mode of construction are also the largest; as time goes on they gradually become smaller. In the very early walls also the stones are split off the rock with wedges, and not cut with any iron tool. The stones are put together without mortar or cement of any kind, and are

supported by their own weight only. This earliest style is believed to have been continued to about a century after the time of Romulus.

The next division differs but slightly from it, the only difference is that the stones are smaller and not exclusively of tufa. The peperino from Albano now comes into use.

The earliest example after the wall of Romulus is the wall of the kings in the Aventine, sometimes attributed to the Latins when they first settled on this hill, and the celebrated Agger of Servius Tullius; the Pulchrum Littus on the bank of the Tiber, and the wall of the kings under the church of St. Anastasia on the Palatine, by the side of the Circus Maximus. Portions of the old walls of the time of the kings against the cliffs of the hills in various parts of Rome also belong to this second division of the Etruscan style of construction, the stones being gradually smaller as the buildings were later. In the later buildings of this style the stones are cut, and not merely split.

The same style is continued in the early part of the republic. The substructure of the Tabularium on the Capitol and the Mamertine Prison are fine examples. In the time of Camillus, after the capture of Veii, there is a marked improvement in the art of building; the stones are well cut with the saw, and closely fitted together, as in the triple arch of the Cloaca Maxima on the bank of the Tiber, inserted in the Pulchrum Littus.

The three temples in the Forum Olitorium, now in the church of St. Nicolas in Carcere, both in the crypt and in the walls, and on the roof, all belong to this style, though not exactly of the same date. These are of the earliest stones, either tufa, or peperino, or gabine, not travertine. The arcades of the earliest aqueducts, the Appia and the Marcia, are of the same style; that of Claudius is of later character, though still of large stones, and looking a good deal like the earlier ones at first sight, but the material is travertine. This mode of construction continued for a long period, and to a certain extent continues still where similar building material is found.

The walls of Aurelian were chiefly built of brick, in some parts it was a mixture of rough stone and brick in alternate layers at regular intervals.

At a later period the Romans adopted two kinds of construction the incertum, or antiquum, composed of small rough pieces placed irregularly, and imbedded in a large quantity of mortar:

and the reticulatum, composed of stones, cut and squared, but joined so that the line of the joining formed a diagonal, which gave to the walls the appearance of net-work. Vitruvius says, that this mode of building was the most common in his time; several examples of it still remain: one may be seen in that part of the walls of Rome called the Muro Torto. The Greeks gave it the name of dictyotheton, synonymous with net; they also communicated to the Romans their emplecton. Another structure of which the Romans made great use, and which was one of the most durable of all, was that composed of long flat tiles; this was called opus lateritium. Canina distinguishes five species of Roman masonry: (1) when the blocks of stone are laid in alternate courses, lengthwise in one course and crosswise in the next: this is the most common. (2) When the stones in each course are laid alternately along and across: this construction was usual when the walls were to be faced with slabs of marble. (3) When they were laid entirely lengthwise; (4), entirely crosswise. (5) When the courses are alternately higher and lower than each other, as in the temple of Vesta, over the Tiber. Rome was encircled with walls at three different periods. These were the Wall of Romulus, B.C. 752; the Walls of Servius Tullius, B.C. 578; the Walls of Aurelian, A.D. 272. The direction of the Wall of Romulus is described by Tacitus. It commenced at the Forum Boarium, and ran along the foot of the Palatine, having the valley afterwards occupied by the Circus Maximus on the right, as far as the altar of Consus, nearly opposite to the extremity of the circus; thence it turned round the southern angle of the Palatine, followed the foot of the hill nearly in a straight line to the Curiæ Veteres, which stood not far from the site of the Arch of Constantine; thence descended again on the other side to the angle of the Forum, which was then a morass. Portions of this wall have been discovered and laid bare on the Palatine hill. The Wall of Servius Tullius was seven miles round, and enclosed seven fortified villages in one city. Starting from the agger, or mound, which was raised by Servius Tullius across the broad table-land formed by the junction of the Quirinal, Viminal, and Esquiline hills, the walls of Servius ran along the outside edge of the Cælian and Aventine hills to the river Tiber by the Porta Trigemina; from this point to the Porta Flumentana, near the S.W. extremity of the Capitoline hill, there appears to

have been no wall, the river itself being considered a sufficient defence. At the Porta Flumentana the fortifications again commenced; and ran along the outside edge of the Capitoline and Quirinal hills, till they reached the northern extremity of the agger at the Porta Collina.*

The Wall of Aurelian. This wall was thirteen miles long and eighty feet high. It contained corridors for the sentinels, and towers at equal intervals. This wall is partially the same as that which surrounds the modern city of Rome, with the exception of the part beyond the Tiber. The Janiculum and the adjacent suburb was the only portion beyond the Tiber which was included within the fortifications of Aurelian. On the left bank of the Tiber the wall of Aurelian embraced on the north the Collis Hortulorum or Pincianus, on the west the Campus Martius, on the east the Campus Esquilinus, and on the south the Mons Testaceus.

MORTAR.-The perfection of that of the ancients has passed into a proverb. The Egyptians never employed it in their great constructions; but other monuments preserve traces of it: the pyramids were formerly covered with a coating which supposes its use. That plaster, lime, bitumen were employed in the arts, is attested by numerous examples. The Greeks and Etruscans were also acquainted with it, evideuces of which are to be seen in a reservoir at Sparta, built of stones, cemented together; and in the sepulchral vaults of Tarquinii, which are plastered with stucco, covered with paintings. Lime mortar was not brought into general use at Rome until two or three centuries before the Christian era; the earliest dated example of the use of lime is believed to be the Emporium on the bank of the Tiber, B.C. 175. Necessity must have made the use of mortar familiar to every people. Time, which has hardened it, has caused it to be considered more perfect than the modern.

Its

* By the excavations lately made at Rome, it has been clearly shown that Servius Tullius did not build one continuous wall seven miles in extent, as is shown on most of the German and English maps, of even recent days, but that he simply connected together the several fortified hills or camps, by a series of short aggeres across the valleys. "To demonstrate this plain fact," says Mr. Parker, "seven pits were dug in a line across the valley, from the foot of the Cælian on the east to that of the Aventine on the west. In each of these pits the agger was found with a wall on the outer side of the agger, or great bank of earth."