Subsequently, rain and rivers have made gullies in the plain. The communities which inhabited the detached hills and project ing ridges which later on formed the city of Rome were in a specially favourable position. These hills (especially the Palatine, the site of the or=dinal settlement) with their naturally steep sides, partly surrounded at the base by marshes and situated not far from the confluence of the Anio with the Tiber, possessed natural advantages not shared by the other primitive settlements of the district ; and their proximity to one another rendered it easy to bring them into a larger whole. The volcanic materials available in Rome and its neighbourhood were especially useful in building. The tufa, speronf: and peperino were easy to quarry, and could be employed by those who possessed comparatively elementary tools, while travertine, which came into use later, was an excellent building stone, and the lava (selce) served for paving stones and as material for concrete. The strength of the renowned Roman concrete is largely due to the use of pozzolana (see PUTEOLI), which also is found in plenty in the Campagna.
Between the volcanic tract of the Campagna and the sea there is a broad strip of sandy plain, evidently formed merely by the ac cumulation of sand from the sea, and constituting a barren tract, still covered almost entirely with wood as it was in ancient times, except for the almost uninterrupted line of villas along the ancient coast-line, which is now marked by a line of sandhills, some m. or more inland. (See LAVINIUM, TIBER.) This long belt of sandy shore extends without a break for a distance of above 3o m. from the mouth of the Tiber to the promontory of Antium (Porto d'Anzio), a low rocky headland, projecting out into the sea, and forming the only considerable angle in this line of coast. Thence again a low sandy shore of similar character, but with extensive shore lagoons which served in Roman times and serve still for fish breeding, extends for about 24 m. to the foot of the Monte Circeo (Circeius Mons, q.v.). The region of the Pomptine marshes (q.v.) occupies almost the whole tract between the sandy belt on the sea-shore and the Volscian mountains, extending from the south ern foot of the Alban hills below Velletri to the sea near Ter racina.
ft. wide, which ran, not at the bottom of the valleys, where there were sometimes streams already, and where, in any case, erosion would have broken through their roofs, but along their slopes, through the less permeable tufa, their object being to drain the hills on each side of the valleys. They had probably much to do with the relative healthiness of this district in early times. Some of them have been observed to be earlier in date than the Via Appia (312 B.c.). When they fell into desuetude, malaria gained the upper hand, the lack of drainage providing breeding places for the malarial mosquito. Remains of similar drainage channels exist in many parts of the Campagna Romana and of southern Etruria (especially to the north of Veii) at points where the natural drainage was not sufficient, and especially in cultivated or inhabited hills (though it was not necessary here, as in the neighbourhood of Velletri, to create a drainage system, as streams and rivers were already present as natural collectors), and streams very frequently pass through them at the present day. The drain age channels which were dug for the various crater lakes in the neighbourhood of Rome are also interesting in this regard. That of the Alban lake is the most famous; that of Nemi has been cleared in connection with the partial drainage of the lake, and found to be precisely similar; but all the other crater lakes are similarly provided. As the drainage by cuniculi removed the moisture in the subsoil, so the drainage of the lakes by emissaria, outlet channels at a low level, prevented the permeable strata below the tufa from becoming impregnated with moisture which they would otherwise have derived from the lakes of the Alban hills. The slopes below Velletri, on the other hand, derive much of their moisture from the space between the inner and outer ring of the Alban volcano, which it was impossible to drain ; and this in turn receives much moisture from the basin of the extinct inner crater. (See R. de la Blanchere, in Dictionnaire des Anti quites, s. vv., Cuniculus, Emissarium.) Prehistoric Remains.—Numerous isolated Palaeolithic ob jects of the Mousterian type have been found in the neighbour hood of Rome in the quaternary gravels of the Tiber and Anio; but no certain traces of the Neolithic period have come to light, as the various flint implements found sporadically round Rome probably belong to the period which succeeded Neolithic (called by Italian archaeologists the Eneolithic period) inasmuch as both stone and metal (not, however, bronze, but copper) were in use.