The peculiar physical features of the district have had no little influence in determining the mode in which the population was grouped in ancient times. Everywhere we find the hills of Rome reproduced on a reduced scale. Small isolated flat-topped hills, irregularly divided by deeply cut watercourses, and edged with steep low cliffs, afford numerous sites for the settlement of limited independent communities. Such are the hills on which Laurentum, Lavinium, Fidenæ Antemnæ, Ficulea, Crustumerium and Gabii stood, and similar places abound in many parts of the district. Such hills afforded suitable sites for the small fortified towns with which ancient Latini was thickly studded. Their sides can be easily scarped so as to afford a natural line of defence, and they are in general fairly supplied with water from numerous land springs. Thus, although the general aspect of the Campagna is that of a plain country, yet the main level of its surface is broken by numerous deep gullies and groups of hillocks. The tertiary marine strata, already described as forming the Janiculum and other hills upon the right bank of the Tiber, do not rise to the surface in the Campagna, except on the flanks of the Æquian and Sabine hills. These hills themselves consist of great masses of Apennine limestone jutting out here and there into the spurs upon which some of the more considerable cities of the Latin confederacy stood, as Tibur, Præneste, Bola and Cameria. The Alban Hills form a totally distinct group, consisting of two principal extinct volcanic craters somewhat resembling, in their relations to each other, the great Neapolitan craters of Vesuvius and Somma. One of them lies within the embrace of the other, just as Vesuvius lies half enclosed by Monte Somma. The walls of the outer Alban crater are of peperino, while those of the inner are basaltic. Both are broken away on the northern side towards Grotta Ferrata and Marino, but on the southern side they are tolerably perfect. From the legendary times, when Latinus, Evander, Æneas, and the rest of Virgil’s heroes are supposed to have occupied the great plain of Latium, down to the final settlement of the district by its subjection to Rome in B.C. 338, the Roman Campagna was peopled by communities chiefly living in towns. Etruria on one side and Latium on the other, contained confederacies of independent cities, with one or other of which the Romans were constantly at war. Etruria gave way first, and after the fall of Veii in B.C. 395, the Roman dominions extended northwards as far as the Lago Bracciano and Civita Castellana.