Beyond the tower of the Pignattara, are a great number of little ruins, mostly of rubble, with a facing of reticulated work in tufo, just of the sort which Vitruvius describes as calculated to last eighty years; yet without being very thick, these walls have probably seen twenty such periods. Most of these buildings have been rectangular, but there is one circular brick building, and there is also a fragment constructed of large blocks of peperino, probably of an early date, and some constructions of _opus incertum_. Leaving the Præneste road, and turning to the left, I passed another piece of an aqueduct, not rising above the more elevated parts of the Campagna, but which from its position, I should conclude not to be of the same work with a similar piece which I had before left on the right. The remains of both are of rubble-work. This is supposed by Nibby to be the Aqua Alexandrina. Some time after, returning towards Rome, I reached a large round building situate on the ancient Via Prenestina, a road which is now little used, called Torre degli Schiavi, or otherwise the temple of Hope. It is a large, circular, domed, brick building; with two ranges of corbels for cornices, and indications of a large base moulding. The brickwork is not very good. Internally, there are four niches, two small arched recesses, one larger one, and opposite to this last, the doorway. It is of better design than the Torre Pignattara, and has had a portico in front, so that it was almost a miniature of the Pantheon. Some of the stucco remains, and traces of the ornaments, and even of figures, may be observed upon the dome. There appears to have been a range of these figures encircling the dome at the springing, and over them a large ovolo, these eight arches (all in painting), and over these other ornaments. Everything is too much decayed to enable us to judge of the effect, or to fix upon a period for the execution. Some figures of saints, evidently of a later date than the paintings just mentioned, prove it to have been used as a Christian church, which was also the case with the Torre Pignattara. The dome is lightened, as in that building, by the use of pots. The foundations shew that it had a portico, which like that of the Pantheon, contained a large niche on each side of the entrance into the building. There is a circular vault below, supported on a central pier. Several fragments of walls, and remains of foundations may be traced in the neighbourhood, and many of the buildings must have been of considerable size. There is one arrangement which occurs several times here and elsewhere; two, three, or even four, parallel vaults are found below, each of these vaults being sometimes divided into two lengths, by a cross wall; and just as many chambers above, which also have been vaulted. In each of the lower vaults, there appears to have been a door at one end, and no other opening; the upper rooms are in most instances,