In these great disasters the inhabitants are afforded an opportunity of exhibiting their valour, and it is always the most energetic who succeed in protecting their property from being washed away by the floods. During the flood just referred {212} to, the inhabitants of the little town of Ostiglia fought successfully with the rising waters, whilst many of their neighbours succumbed. The town stands close to the froldo, and there is no second line of dykes to protect it. The dyke threatened to give way. The inhabitants at once set about throwing up a second barrier. All the able-bodied men of the place, 4,000 in number, turned out to work, headed by their mayor. They worked day and night, and, as the floods carried away the old dyke, the new one rose in its rear. The victory was won; the floods retired, and their houses were safe.
Some of those breaches in the dykes have led to permanent changes in the course of the river, and these divagations have been most considerable in the delta. During the time of the Romans, and up to the thirteenth century, the Po di Volano was the principal branch of the river, whilst now it has dwindled down to an insignificant ditch which can hardly be traced through the swamps of Comacchio. Two other branches, farther to the south, are used now as carriage roads. In the eighth century the Po di Primaro, which enters the sea to the north of Ravenna, took the place of these old channels. Another bifurcation ensued in 1152, when the embankment at Ficcarolo was destroyed, it is said, by the people living above that town, and the main channel of the river, the Maestra, deserted the walls of Ferrara in the midst of its swamps, and united itself with the channels of the Adige. Breaches in the embankments usually take place in October or November, and generally at the same places. The danger is always greatest at Corbola, where the Po di Maestra bifurcates.
The Adige is quite as great a wanderer as the Po. Scarcely has that river left its defile, or chiusa, of calcareous mountains and the fortifications of Verona than it begins its erratic course over the plain. In the time of the Romans the Adige flowed much farther to the north, along the foot of the Euganean Hills, and entered the sea at Brondolo. In 587 the river broke through its embankments, and its main branch took the direction which it maintains up to the present day, entering the sea at Fossone. But new channels opened repeatedly towards the south, until the Adige and Po conjointly formed but one delta. The Polesina of Rovigo, between the two rivers, and that of Ferrara, are low tracts of alluvial land. The courtyard of the Castle of Ferrara, which occupies one of the most elevated sites in these plains, is nine feet lower than the highest level of the Po when flooded.
The frequent inundations caused by the Po and the numerous changes of its bed, by spreading the alluvium all over the country, have raised the whole of the plains to about the same level. But now, when all the arms of the Po are confined within embankments, most of the alluvium brought down by the floods is deposited on the coast of the Adriatic. The land, therefore, gains much more rapidly upon the sea than it did formerly. The series of dunes marking the ancient shore now lies fifteen miles inland, and the new land formed annually is estimated at 280 acres. In exceptional years the quantity of solid matter carried by the river into the sea amounts to 3,531,000,000 cubic feet; on an average it is 1,623,000,000 cubic feet, sufficient to form an island ten square miles in area in ten feet of water. The Po, next to the Danube, is the most active geological agent amongst all the rivers {213} entering the Mediterranean.[66] The Rhone is inferior to it, and so is the Nile. At the present rate of progress, the Po, in the course of a thousand years, will throw a tongue of land six miles wide across the Adriatic, converting the Gulf of Trieste into an inland sea.
Northern Italy, in addition to these numerous rivers, possesses one of the most extensive systems of canals in the world, which has served as a pattern to all the rest of Europe. Lombardy, portions of Piemont, the Campagna of Turin, the Lomellina on the Ticino, and the Polesinas of Ferrara and Rovigo possess a wonderful ramification of irrigation, which carries fertile alluvium to the exhausted fields. In the Middle Ages, when the remainder of Europe was still shrouded in darkness, the Lombard republics already practised the art of irrigation on the vastest scale, and drained their low-lying plains. Milan, after she had thrown off the yoke of her German oppressors, towards the close of the twelfth century, constructed the Naviglio Grande, a ship canal derived from the Ticino, thirty miles distant—probably the first great engineering work of the kind in Europe. In the beginning of the thirteenth century the superabundant waters of the Adda were utilised in filling the Muzza Canal. The same river, at a subsequent period, was made to feed another canal, the Martesana, which was constructed by the great Leonardo da Vinci. The art of surmounting elevations of the ground by means of locks had been discovered by Milanese engineers about a century before that time, and was applied to the construction of secondary canals. Amongst works of more recent date are the naviglio from Milan to Pavia; the Cavour Canal, fed by the Po, below Turin; and the Canal of Verona, derived from the Adige.[67]
Not only the rivers of Northern Italy, but also the springs, or fontanelle, however small, which burst forth at the foot of the Alps, are utilised for purposes of irrigation. Virgil alludes to these springs in his Bucolics, where he says, “Children, stop the water; the meadows have drunk enough.” Lombardy is indebted to these springs for her fine prairies, or marcite, which sometimes yield eight crops a year. The great Adriatic plain has indeed undergone vast changes through the work of man. Originally it was a swamp surrounded by forests and heaths, but is now one of the best-cultivated countries of Europe. One of its great features consists in plantations of mulberries, the uniformity of which is relieved in many districts—and especially in the Brianza of Como, that {214} garden of Italy—by groups of tall trees, little lakes, and sinuous valleys. There still remain extensive heaths covering the moraines of ancient glaciers, which become more and more sterile from year to year; but the engineers are considering schemes for irrigating them by means of the fertilising waters of the Alpine lakes.
The irrigated area in the valley of the Po nearly amounts to 5,000 square miles, and the water it absorbs every second is estimated at 35,000,000 cubic feet, equal to about one-third of the volume of the Po. If the proposed works of irrigation are carried out, the Po, which now plays so important a part in the economy of the country by its floods and alluvial deposits, will be reduced to the dimensions of a small river.
The evaporation from the numerous rivers and canals of the country fills the air with moisture. Rains are less frequent than on the Atlantic coasts of England and France, but the clouds, driven by southerly winds against the cool slopes of the Alps, discharge themselves in torrents. The quantity of rain that falls in the upper Alpine valleys equals that of the most humid districts of Portugal, the Hebrides, and Norway, and the rainfall in the plains of Lombardy is equal to that of Ireland. The annual rainfall in the basin of the Piave is estimated at five feet, exclusive of what may evaporate or be absorbed by plants. These rains are not confined to certain seasons, though it has been observed that they are most abundant in May and October, and least so in February and July.[68]
As regards the direction of the winds, the great plain bounded by the Apennines and the Alps resembles an Alpine valley, the winds either blowing up it from east to west, or in an inverse direction. The winds descending from the Alps rarely bring rain, for they have deposited their moisture on the western slopes, but those coming from the Adriatic are generally charged with moisture. Nevertheless, owing to the great extent of the plains and the numerous breaks in the mountain chains, this rule is frequently interfered with. In the Alpine valleys the ascending and descending currents are far more regular, and the navigators on the lakes fully avail themselves of this circumstance.
The forty-fifth degree of north latitude intersects the valley of the Po, but the climate, nevertheless, is not as mild as might be expected from this circumstance, and the range of temperature is great. In the Val Tellina the temperature sometimes rises above 90°, and frequently fails below freezing point. In the plain the climate is less austere, but it is notwithstanding continental in its character; and Turin, Milan, and Bologna are for this reason the least pleasant cities of Italy to live in. A few favoured spots on the Alpine lakes, such as the Borromean Islands, are an exception to this rule, and enjoy an equable climate, thanks to the moderating influences of a vast expanse of water. In the Gulf of Pallanza the thermometer never falls below 40° F., and we must go as far as Naples if we would meet with a climate equally favourable to vegetation. Venice, too, is a privileged spot, thanks to the vicinity of the Adriatic, and is healthy, too, in spite of the lagoons {215} which surround it. It is remarkable that these brackish lakes and swamps of Northern Italy do not give rise to the dreaded malarial fevers. Venice undoubtedly owes its healthiness to the tides, which are higher there than in the Tyrrhenian Sea, and perhaps, also, to the cold winds descending from the Alps. Comacchio, too, is a healthy place, and young natives of the Polesina suffering from consumption are sent there to recover their health. Wherever the engineers have cut up the connection between the lagoons and the open sea, marsh fever has made its appearance. The swamps of Ravenna and Cervia breed malignant fevers, especially where avaricious landowners have cut down the protecting rows of pines and oaks. A heavy miasmal air hangs likewise over the environs of Ferrara and Malalbergo, at the head of the Paduan delta.