BEGINNING with the Porta del Popolo, and following in the direction of the sun, I have taken you in succession out of the different gates; but we will now set out by the gate of St. Sebastian, and return by that of San Giovanni, which would precede it in regular order. Before arriving at the gate, we meet with three objects deserving notice, which though within the walls, were too distantly situated to be included in our former walks. The first of these is the great ruin of the Baths of Caracalla. The general plan of the Roman _thermæ_ seems to have been that of a large, rectangular, central building, placed in a spacious enclosure, surrounded by smaller edifices, and on one side of this court there was a large open theatre, or rather _cavea_. This disposition may be traced in the three which exist the most perfectly; of the others we have not sufficient materials to decide whether it was adopted or not; and only conclude it to have been so from analogy. It is very conspicuous in the Baths of Caracalla, only the _cavea_, instead of being semicircular, is in the form of half a stadium, or circus. The ruins of these baths are very considerable, and are impressive by their vast square mass; and internally, the immense piles of brick and rubble give it a solemnity of character with which the deep, still blue of an Italian sky is in perfect harmony, though the tints of the ruin are of rich and glowing colours. However often one may visit them, it is always with repeated pleasure that we ramble among their massive constructions. The great central chamber seems, like the great hall still remaining in the baths of Dioclesian, to have been covered with groined arches. It was probably the first instance of groined arches covering a space of any considerable extent, and as there can be no doubt that so striking a novelty would be admired and repeated, we are not surprised at finding it in all the later thermæ. It is true that Palladio introduces this disposition in his plans of all the baths, but he appears in this, as in some other instances, to have supplied the deficiencies of one, by adapting to it the parts of another, without sufficient authority. The great central building was composed internally of two large colonnaded courts, one at each end, and vast halls, and a multitude of smaller chambers between, and on each side of them; on each side of the outer circuit of buildings, there seem to have been other edifices disposed circularly, and an octagonal room, which has the appearance of a hall of entrance, occurred at each end. In one of these the celebrated _Toro Farnese_ is said to have been found, but I believe the fact is doubtful. We find in the part which now remains horizontal lines, which probably mark the situations of the marble cornices, and many other indications of the enrichments which have been taken away: we trace also pipes in the wall in various places, some apparently intended to take off the