The road beyond this rises from the valley of the Almo, and passes over a kind of plateau. It is hemmed in on either side by high ugly walls, shaggy with a profusion of plants which affect such situations. The wild mignonette hangs out its pale yellow spikes of blossoms, but without the fragrance for which its garden sister is so remarkable; and the common pellitory, a near ally of the nettle, which haunts all old ruins, clings in great masses to the crevices, its leaves and ignoble blossoms white with the dust of the road. Here and there a tall straggling plant of purple lithospermum has found a footing, and flourishes aloft its dark violet tiara of blossoms; while bright tufts of wall-flower send up their tongues of flame from an old tomb peering above the wall, as if from a funeral pyre. The St. Mary thistle grows at the foot of the walls in knots of large, spreading, crinkled leaves, beautifully scalloped at the edges; the glazed surface reticulated with lacteal veins, retaining the milk that, according to the legend, flowed from the Virgin's breast, and, forming the Milky Way in mid-heaven, fell down to earth upon this wayside thistle. Huge columns of cactuses and monster aloes may be seen rising above the top of the walls, like relics of a geologic flora contemporaneous with the age of the extinct volcanoes around. But the most curious of all the plants that adorn the walls is a kind of ivy which, instead of the usual dark-greenish or black berries, bears yellow ones. This species is rare, but here it occurs in profusion, and is as beautiful in foliage as it is singular in fruit. The walls themselves, apart from their floral adorning, are very remarkable, and deserving of the most careful and leisurely study. They are built up evidently of the remains of tombs; and numerous fragments of marble sarcophagi, pillars, inscriptions, and rich sculpture are imbedded in them, suggestive of a whole volume of antiquarian lore, so that he who runs may read.

On the right of the road, in a vineyard, are several Columbaria belonging to the family of Cæcilius, an obscure Latin poet, who was a predecessor of Terence, and died one hundred and sixty-eight years before Christ; and on the left are the Columbaria of the freedmen of Augustus and Livia, divided into three chambers. These last when discovered excited the utmost interest among antiquarians; but they are now stripped of all their contents and characteristic decorations, and the inscriptions, about three hundred in number, are preserved in the museums of the Capitol and Vatican. On the same side of the road, in a vineyard, a Columbarium was discovered in 1825 belonging to the Volusian family, who flourished in the reign of Nero; one of whose members, Lucius Volusius, who lived to the age of ninety-three, was extolled on account of his exemplary life by Tacitus.

On the same plateau is the entrance to the celebrated Catacombs of St. Calixtus. It is on the right-hand side of the road, about a mile and a quarter from the present gate, and near where stood the second milestone on the ancient Appian Way. A marble tablet over the door of a vineyard shaded with cypresses points it out to the visitor. The rock out of which this and all the Roman Catacombs were hewn seems as if created specially for the purpose. Recent geological observations have traced in the Campagna volcanic matter produced at different periods, when the entire area of Rome and its vicinity was the seat of active plutonic agency. This material is of varying degrees of hardness. The lowest and oldest is so firm and compact that it still furnishes, as it used to do, materials for building; the foundations of the city, the wall of Romulus, and the massive blocks on which the Capitol rests, being formed of this substance. Over this a later stratum was deposited called tufa granolare, consisting of a similar mechanical conglomerate of scoriæ, ashes, and other volcanic products, but more porous and friable in texture. It is in this last formation, which is so soft that it can be easily hollowed out, and yet so solid that it does not crumble, that the Catacombs are invariably found. There is something that appeals strongly to the imagination in the fact that the early Christians should have formed the homes of their dead and the haunts of their faith in the deposit of the terrible volcano and the stormy sea! The outbursts of the Alban volcanoes were correlated in God's scheme of providence with the outbursts of human fury long ages afterwards; and the one was prepared as a means of defence from the other, by Him who maketh His ministers a flaming fire.