In order to attain a correct idea of the ground-plan, we must proceed to the space in the centre, enclosed on the side towards the road by a high wall furnished with window niches for the reception of statues. This was the great swimming-bath, as is proved by the excavations, which have revealed the deep level of the original floor. Beyond this are small rooms where the bathers were oiled and shampooed; beyond these again is the GRAND PERISTYLIUM, enclosed with pillars and a portico, in which were performed the athletic exercises; adjoining were the Women's Baths. Returning through the HEMICYCLIA, we enter the PINACOTHECA, or Fine Art Gallery. This brings us to the TEPIDARIUM, or Warm Bath, with four hot baths, CALDARIA, at the corners, from which the SUDATORIUM, or Sweating Room, was entered. This was called the CELLA SOLEARIS. The roof was supported by bars of brass interwoven like the straps of a sandal. Vitruvius tells us that the Sudatorium ought to be circular, with a circular window in the centre of the dome, with a shutter to be opened or shut,--thus controlling the atmosphere as required. The Solearis was considered a great architectural feat, and inimitable. Of this grand rotunda only four piers are left, but these are sufficient to give an idea of its size; and it was to the Baths of Caracalla what the Pantheon was to the Baths of Agrippa: that is the only perfect part of those baths left; this is the only part of these baths wanting. The mosaics of the pavement have sunk down, as it were, in the form of troughs, in consequence of the piers on which the arches rested, as on a sort of grating, having been broken when the latter fell in, and not being properly shored up when excavated. The remainder of the building recently excavated corresponds with the parts we have described. Some of the beautiful mosaic pavements may be seen in the Lateran and Borghese Villa Palaces. _Above the baths, on an eminence of the Aventine, is the_ CHURCH OF S. BALBINA, supposed to date from the sixth century. There is nothing of interest in the church itself, but from the tower a fine prospect is enjoyed of the surrounding district. The convent and church have been turned into a penitentiary and a barrack. _Resuming our ramble along the main road, on the right is the_ CHURCH OF SS. NEREO E ACHILLEO, founded by Leo III. (795-816). It contains an enclosed choir with reading-desks. The tribune mosaic is of the founder's time, and represents the Transfiguration and Annunciation. The episcopal chair is that from which S. Gregory read his Twenty-eighth Homily. The church is on the site of the TEMPLE OF MARS,