The execution of this vast scheme is no doubt attended with immense difficulties, not the least amongst which are the annual floods of the Tiber. Ancient writers tell us that these inundations were dreaded not only because of the damage done directly, but also because of the great quantities of animal and vegetable deposits which remained in the fields after the subsidence of the waters. The nature of these floods has continued the same down to the present time. At Rome, though its distance from the sea is only twenty-two miles, the river frequently rises forty or fifty feet, and in December, 1598, it rose sixty-five feet ! How is this huge volume of water to be disposed of after it has passed beneath the bridges of Rome? If the destruction of the forests in the Apennines is one of the principal causes of these floods, will it be sufficient to replant them? Or would it be preferable to restore some of those ancient lakes into which numerous rivers discharged themselves, which now take their course to the sea? The difficulties are great indeed, for the western slope of the Apennines is exposed to the rain-bearing westerly and south-westerly winds, and the floods of every one of the numerous tributaries of the Tiber take place simultaneously, and combine to form one vast inundation. It is by no means difficult to account for the great floods of the Tiber which take place in winter, but the condition of the river during summer has for a long time baffled inquiry. The level of the river during the dry season is far higher than could possibly be accounted for by the small quantity of rain which falls within its basin. Its volume in summer is never less than half its average volume, a phenomenon not hitherto observed in the case of any other river. The Seine has a basin five times larger than that of the Tiber, and its average volume is almost double; yet, after a continuance of dry weather, its volume is only a third or fourth of the Italian river. This perennity of the Tiber can only be accounted for by assuming that it is fed, during the dry season, from subterranean reservoirs, in which the water is stored up during winter. These reservoirs must be very numerous, if we are to judge by the numerous “sinks,” or “swallows,” met with on the calcareous plateaux of the Apennines. One of these sinks, known as the “Fountain of Italy,” near Alatri, close to the Neapolitan frontier, has the appearance of a huge pit, 160 feet in depth and 300 feet across. Its bottom is occupied by a forest, and numerous springs give rise to luxuriant herbage, upon which sheep lowered by means of ropes feed with avidity. It is from sinks like this that the rivers of the country, the Tiber and the Sacco, are fed. It has been computed by Venturoli and Lombardini, the engineers, that about three-fourths of the liquid mass of the Tiber during winter are derived from subterranean lakes hidden in the depths of the Apennines.