=5. The Tiber and Its Valley.=--Near at hand, of course, is the Campagna itself, a series of gentle ridges, covered at this epoch with one long series of delightful suburban villas and thrifty produce farms, sometimes grouped into rich little villages.[2] In a general direction of north to south the Tiber flows along the western skirts of Rome, with only a minor settlement on the western banks. If it ran by a less famous city, the Tiber would pass for a rather ordinary stream. Its yellow, turbid waters come with such force from the Apennines that there can be little navigation for part of the year beyond the point where the Anio flows into it from the east, about three miles above Rome. Grain and timber can, however, be floated down on barges, and when the mountain snows are melting the river swells to a truly dangerous size, flooding all the lowlands near the city and sometimes, despite a careful system of dykes, causing freshets which are simply ruinous to large sections of the metropolis inhabited by the very poor. The Emperors Augustus and Tiberius set up a regular board of “Tiber Commissioners” to keep the rebellious river in bounds, but their efforts are still often vain. Between Rome and Ostia the Tiber is indeed navigable at most seasons for the smaller kind of vessels, but, as will be seen, Rome is scarcely a first-class seaport; however, special river craft easily bring up heavy freight from Ostia--an enormous economic advantage for the great city. =6. A View over Rome from the Campus Martius.=--Before descending into the city it is well to ascend some height or lofty building well to the western verge of the _Campus Martius_ (“Field of Mars”) at the great bend of the Tiber as it sweeps by its levees. Before the onlooker there spreads what seems at first an indescribable confusion of enormous buildings, gilded roofs, stately domes, serried phalanxes of marble columns and far-stretching porticoes, some on level ground, others upon the summits or clinging to the slopes of several hills. Mixed with these are an incalculable number of red-tiled roofs obviously covering more humble private structures. Here and there, mostly on the outskirts, are also broad patches of greenery, public parks, and private gardens.