The ancient road to Tivoli passed over this bridge, and some fragments of the ancient work remain. At a very small distance is a cavern, partly, if not entirely artificial, with some niches on the side, called the Temple of the World; and on ascending the hill, we find a domed, octagonal hall, denominated Tempio della Tosse, but supposed by antiquaries to have derived its name from an ancient Tivolese family. Its ancient destination is unknown, but in after-times it appears to have been converted into a church, and retains some traces of such an appropriation. Our next object is the Villa of Mæcenas, where the remains are more considerable than in any other, exhibiting, besides the usual substructions, part of a court surrounded by half columns and arches, and a long gallery, whence you command the valley below. The ancient Roman road passed under this villa, part of which was lately appropriated to a foundery for cannon, and an abundant stream of water still dashes through the deserted vaults. Within the city, a circular wall of reticulated work, at the back of the cathedral, is supposed to mark the position of the Temple of Hercules; and a double range of vaults of considerable length, is known by the name of the Portico of Hercules. It has square pilasters in front, which serve as buttresses to the vaulting. The construction of the Villa d’Este is on a scale which may entitle it to be mentioned among these ancient productions. Terrace rises above terrace, and a copious supply of water rushes down an artificial rock 34 feet in height, spreading in a beautiful manner as it descends, while the whole is crowned by the long façade of the palace. LETTER XXXVI. SUBIACO—PALESTRINA. _Rome, 31st May, 1817._