In speaking of lakes, we must resume our twofold division of the peninsula. On the Alpine slopes of the great valley of the Po, the granitic and ancient limestone rocks break into vast chasms at right angles to their general direction, in which the waters of the rivers that flow downwards to join the Po accumulate and form those lakes so well known to all lovers of natural beauty. Such are Lake Benacus (Lago di Garda) formed by the waters of the Mincius; Larius (Lago di Como) by those of the Adda; Verbanus (Lago Maggiore) by those of the Ticino; not to mention the lakes of Lugano, Orta, and others, smaller, indeed, but hardly less beautiful. But Apennine Italy, considering the great extent of its mountain districts, does not present many considerable lakes. Nor are these formed by the accumulated waters of rivers flowing through them, like the lakes of northern Italy or Switzerland. For the most part, like the lakes of Greece, they have no visible outlet, but lose their waters partly by evaporation, partly by underground fissures and channels. The Fucine Lake in the Æquian hills feeds the Sangro, and Lake Bradanus in the south feeds the river of the same name. But the celebrated Lake Trasimene in Etruria, and the lakes of the volcanic district, as the “great Volsinian Mere,” the lakes of Alba, Nemi, Amsanctus, and others, have no visible outlet. These, in fact, are the craters of extinct volcanoes. Roman history contains legends which relate to the artificial tapping of these cauldrons; and some of the tunnels cut through their rocky basins still remain. The abundance of water which is poured over the hills is apt to accumulate in marshy swamps in the low districts towards the sea. Such is the case along the lower course of the Po, on the coast lands of Tuscany, and in the lower part of the Campagna of Rome. Mantua, which stands a little above the junction of the Mincio with the Po, is surrounded by marshes; and the whole coast between Venice and Ravenna is a swamp. To keep the Po and its tributaries within their channels, the Lombards of the Middle Ages raised embankments on either side of the stream. But these embankments cause the rivers to deposit the whole of the mud with which they are charged within their channels, and the quantity thus deposited is so great that it is necessary to raise the embankments continually. Hence, in the course of centuries, the bottoms of the rivers have been elevated considerably above the plains; so that the streams of Lombardy in their lower course are in fact carried along huge earthen aqueducts. In time, human industry will not be equal to raise these embankments in sufficient strength, and a deluge will ensue more fearful than those which the poet of Mantua seems to have witnessed. EARLY POPULATION OF ITALY