There is nothing to claim your attention in the architecture of the Church of St. Sebastian; but in a subterraneous chapel is a beautiful bust of the saint, by Bernini, full of expression; and here also is the entrance to the most extensive catacombs about Rome. They consist of crooked winding passages in tufo and pozzolana, in three stories, which as the levels are not always exactly preserved, are easily made into seven by those who wish to increase the appearance of the marvellous. The niches for the bodies are mere square recesses, about the length of a human body, and just big enough to receive it; but there are some larger ones forming an arch, at the bottom of which the body was placed: wherever these larger arched niches are found, there is a little apartment, whose rude sides have been coated with stucco. I will not however venture to say that there are no stuccoed rooms without niches, but the two circumstances generally go together. They pretend to have found here, the bodies of 174,000 martyrs. A collection of itself sufficient to stock all Europe with relicks. A little beyond this is the Spoliarium, or Mutatorium; or it is a temple, according to Palladio, or anything else you please. It has been generally supposed to have supplied some purpose dependent on the circus of Caracalla, with which it has however no connexion. It consists of a round edifice inclosed in a court. The central building is formed by a circular wall, with an octagonal pier in the middle supporting a vault; the whole forming doubtless the basement of a large domed hall above, which no longer exists. The work is of rubble, which within the vault is faced with bricks, laid regularly, but with a great deal of mortar; the vault is altogether of rubble. There are niches in the middle pier, and its octagonal form seems not essential, since the vault rises upon a circle described within it. The surrounding wall of the court is built of alternate layers of brick and stone, or rather of tufo, for it hardly deserves the name of stone. Within it, are remains of piers formed of brick only, and there are some vestiges of the vaulting with which the intervening space was covered, forming a continued arcade round three sides of the court, or perhaps all four, but that towards the road is quite destroyed. Close on the outside of this court is a sepulchre, long attributed to the Servilian family, but as the true burying-place of that family has been since found at a considerable distance, and determined by inscriptions, this remains without a name. It is of a square form without and within, and is covered, not with a proper vault, but pyramidally, on the principle of the _dos d’âne_. There are, however, rough arches to some of the openings; a passage is carried all round the building in the thickness of the walls. The whole construction is certainly very singular, and appears to be of high antiquity, but I cannot pretend to assign a probable date.