The Lario, or Lake of Como, which rivals the Maggiore by its beauty, is likewise being gradually silted up. In the time of the Romans the navigation extended as far as Summolacus (lake-head), the modern Samolaco. But the torrent of Mera gradually converted most of the upper extremity of the lake into an alluvial plain, whilst the alluvial deposits carried down by the Adda cut off the remainder from the main body of water. There now remains only the Lacus {200} Dimidiatus, or Lake of Mezzola, which is shrinking from year to year, and will finally disappear altogether. The miasmata rising from the swamps at the mouth of the Adda have frequently depopulated the environs, and the ruined fort of Fuentes, at the mouth of the river, built to defend the Val Tellina, was hardly ever more than a hospital for its fever-stricken garrison.
The south-eastern arm of the lake, that of Lecco, through which the Adda makes its escape to the south, has likewise been divided into a series of separate basins. Nature, which would convert these lakes into bottom-lands at no distant date, is being aided here by the works of man. The barrier which obstructed the free egress of the Adda has been cleared away, the structures of fishermen have been removed, and, in consequence of these and other engineering measures, the once-dreaded rises of the lake have been reduced to a minimum, and the southernmost of the lake basins, that of Brivio, has been converted into dry land. The large Lake of Brianza, which extended formerly far to the south-west, has likewise been partially drained, and there now remain only a few lakelets of small extent.
We know sufficient of the bottom of the Lake of Como to enable us to judge of the manner in which it is becoming gradually filled up with alluvium. The mud deposited in its northern portion has filled up all the original inequalities of the soil, and even in the centre of the lake, and in its south-eastern arm, the bottom is almost a perfect level. In the Como arm, however, which receives no tributary river of any importance, the bottom is still full of inequalities. These differences amply prove to us the geological agency of the rivers, which must terminate in the lake being converted into a bottom-land, with a river flowing through its centre. The third of our diagrams (Fig. 62) shows that the greatest depth now hardly exceeds 1,300 feet, whilst, if we may judge from the slopes of the hills which bound it, the depth in former times cannot have been less than 2,300 feet.
The Sebino, or Lake of Iseo, and the lakelet of Idro, which are fed by the glacier streams of the Adamello, exhibit the same features as the lakes farther to the west. The Benaco, or Lake of Garda, however, the most extensive of these Alpine lakes, is very stable as regards its outline and the configuration of its bottom, a fact sufficiently explained by the small size of its tributary streams as compared with its vast area. The old Alpine lakes of the Venetian Alps have disappeared long ago, and there remain only a few ponds, filling cavities in the dolomitic rocks and peat bogs, to indicate their ancient sites.[64] {201}
Fig. 63.—VILLA SERBELLONI, ON THE PENINSULA OF BELLAGIO, LAKE OF COMO.
These lacustrine basins, like all other reservoirs of the same kind, regulate the outflow of the torrents which empty into them. During the freshets they store up the superabundant waters, and only part with them in the dry season, and upon their difference of level in different seasons depend the oscillations of the emissary rivers which issue from them. In the case of the Lake of Garda, which drains but a small area in proportion to its size, this difference is small, and throughout the year the pellucid waters of the Mincio flow tranquilly beneath the blackened ramparts of Peschiera. Such is not the case as regards either the Lago Maggiore or the Lake of Como, for the volume of water discharged into them is so considerable that their level in summer and winter varies to the extent of several yards, and corresponding differences may be observed in the rivers issuing from them. Lake Como rises no less than 12 feet, and increases 70 square miles in area, whilst the Lago Maggiore sometimes rises 22 feet, and {202} increases to the extent of one-fifth. The volume of the Ticino, when at its highest, almost equals the average volume of the Nile, and if it were not for the regulating influence of the lake from which it issues, it would alternately convert the plains of Lombardy into a sheet of water and leave them an arid tract of land.[65]
The Alpine lakes of Italy thus play an important part in the economy of the country. They render the climate more equable, serve as high-roads of commerce, and, being the centres of animal life, attract a dense population. But it is not this which has rendered these lakes famous, which has attracted thousands of wanderers ever since the time of the Romans, and caused villas and palaces to rise on their shores: it is their incomparable beauty. And, indeed, there are few spots in Europe which bear comparison with the delightful Gulf of Pallanza, over which are scattered the Borromean Islands, or with the peninsula of Bellagio, which may be likened to a hanging garden suspended within sight of the snow-clad Alps, and affording a prospect of the rock-bound shores of the Como Lake, cultivated fields, and numerous villas. Perhaps even more delightful is the peninsula of Sermione, jutting out into the azure waters of the Garda Lake, like the tender stalk of a flower developing into a many-coloured petal.
Most of the lakes in the plain have been drained into the neighbouring rivers. The Lake of Gerondo, mentioned in mediæval records, has dwindled down into a small swamp, or mosi, now, and its populous island of Fulcheria has become merged in the plain of Lombardy. The lakes on the southern bank of the Po, above Guastalla, have likewise been drained; and if the two shallow lakes of Mantua still exist, this is entirely due to the embankments raised in the twelfth century. It would have been much better, and would have saved the city the horrors of many a siege, if these lakes had been allowed to disappear likewise.