Sometimes they are employed in spreading still farther the barren crusts of their peculiar deposit, and sometimes probably in filling up the old channels, after which of course the stream has to find a new one, but as it is rather disposed from the form of the ground to spread over the surface, than to find its way in a single channel, an artificial one has been made for it down to the Anio. These swallows are repeated in different places, so that the stream becomes larger as we ascend, and perhaps where it issues from the little Lago di Solfatara, may be not much inferior in quantity to the New River, but running much faster in a smaller bed. In March I was inclined to call it hot, but I suppose the temperature does not equal 80° of Fahrenheit. Reeds grow abundantly on the banks, and one or two species of conferva, especially an _Oscillatoria_, resembling _C. fontinalis_ of Dillwyn, which is what the books and the guides call bitumen. The lake is a mere pond, but is said to be very deep; the water at the edges is not so hot as where the stream issues from it. Detached bubbles are continually rising in all parts, and when a stone, or even a clod of earth is thrown in, a violent ebullition is produced, which lasts several minutes. Almost close to the lake, there is a ruined building, believed to be the remains of an ancient bath. There are two other lakes, still smaller, but all very deep; the size of all of them is continually diminishing, from the progress of vegetation; and the matted roots of reeds sometimes form floating islands, and extend over the surface of the water. Here, according to the antiquaries, Virgil places the scene where Latinus consulted the oracle of Faunus; but even if we can suppose the plain to have once abounded with wood, a fact which the nature of the soil renders highly improbable, how can we place them _sub altâ albuneâ_, when the country is nearly flat, or how can a spring rising in a deep pool be said to _resound_? But I leave these difficulties to wiser heads, and will continue my route towards Tivoli. At sixteen miles from Rome is the Ponte Lucano, another ancient bridge over the Teverone, but with some modern patching. Close by this is a fine circular monument, with several inscriptions belonging to the Plautian family, which is said to have been originally from Tivoli, but was much distinguished at Rome in the latter part of the republic, and the early part of the empire. It is a very fine object, and its strength and solidity have tempted some of the noble robbers of the lower ages, to convert it into a fortress, of which there are considerable remains at the top, but I could not get into it.