A little farther is the Villa Giulia, which I have already described; and there is another edifice of simple and not unpleasing architecture, attributed to Antonio Sangallo, also belonging to a villa or vigna Giulia. By these, a lane called Via dell’ Arco Scuro, leads to the Aqua Acetosa, a mineral spring on the banks of the Tiber, having very much the taste of ink. I have also mentioned the chapel of St. Andrew, by Vignola, which is the next object in following the road. A little before arriving at the Ponte Molle, we find another chapel of St. Andrew, or rather a monument erected on the spot, where according to tradition, Pius II., in 1463, met the head of the apostle on its arrival at Rome. Upon a square basement, whose height is probably rather greater than its width, is a little edifice with a column in each angle, a doorway between them in each face, and a pediment above; the four fronts being all precisely alike. Over this is an octagonal drum of very small height, and a little, scaly cupola, surmounted by a cross. The composition is simple and pleasing, for a little thing, but it would not do for a large one. The Ponte Molle, the ancient Pons Milvius, is the uppermost of the ancient bridges about Rome over the Tiber. It was originally built in the year of Rome 645; but it is doubtful if anything we see remaining be of that period. Yet there is some ancient work in the piers, which is easily distinguished from the later masonry of the arches, attributed to Nicolas V. Till 1805 it was encumbered by an inconvenient tower at one end; but being at that time damaged by an inundation, the road was straightened, and made more commodious, and the tower converted into a sort of triumphal arch; but it boasts no beauty. After crossing the bridge we will take the right hand road up the hill, which coasts the valley of the Tiber. At the distance of about two miles, we again descend, and the road is cut into the hill, shewing it to consist of a gravel principally composed of rounded pebbles of an argillaceous limestone; near the bottom is the Torre di Quinto, standing, not upon this gravel, but upon a fresh water limestone, like the travertine, or the deposit of the Tartar lake, with similar indications of having been formed on reeds, twigs, &c. This again rests on a volcanic tufo, very unequal in substance and surface. The lower part of the limestone includes numerous fragments of this tufo, but there are none of them in the upper part of the bed. The tower itself is of the middle ages.