§ III. When the eye falls casually on a map of Europe, there is no feature by which it is more likely to be arrested than the strange sweeping loop formed by the junction of the Alps and Apennines, and enclosing the great basin of Lombardy. This return of the mountain chain upon itself causes a vast difference in the character of the distribution of its débris on its opposite sides. The rock fragments and sediment which the torrents on the north side of the Alps bear into the plains are distributed over a vast extent of country, and, though here and there lodged in beds of enormous thickness, soon permit the firm substrata to appear from underneath them; but all the torrents which descend from the southern side of the High Alps, and from the northern slope of the Apennines, meet concentrically in the recess or mountain bay which the two ridges enclose; every fragment which thunder breaks out of their battlements, and every grain of dust which the summer rain washes from their pastures, is at last laid at rest in the blue sweep of the Lombardic plain; and that plain must have risen within its rocky barriers as a cup fills with wine, but for two contrary influences which continually depress, or disperse from its surface, the accumulation of the ruins of ages.
§ IV. I will not tax the reader’s faith in modern science by insisting on the singular depression of the surface of Lombardy, which appears for many centuries to have taken place steadily and continually; the main fact with which we have to do is the gradual transport, by the Po and its great collateral rivers, of vast masses of the finer sediment to the sea. The character of the Lombardic plains is most strikingly expressed by the ancient walls of its cities, composed for the most part of large rounded Alpine pebbles alternating with narrow courses of brick; and was curiously illustrated in 1848, by the ramparts of these same pebbles thrown up four or five feet high round every field, to check the Austrian cavalry in the battle under the walls of Verona. The finer dust among which these pebbles are dispersed is taken up by the rivers, fed into continual strength by the Alpine snow, so that, however pure their waters may be when they issue from the lakes at the foot of the great chain, they become of the color and opacity of clay before they reach the Adriatic; the sediment which they bear is at once thrown down as they enter the sea, forming a vast belt of low land along the eastern coast of Italy. The powerful stream of the Po of course builds forward the fastest; on each side of it, north and south, there is a tract of marsh, fed by more feeble streams, and less liable to rapid change than the delta of the central river. In one of these tracts is built Ravenna, and in the other Venice.
§ V. What circumstances directed the peculiar arrangement of this great belt of sediment in the earliest times, it is not here the place to inquire. It is enough for us to know that from the mouths of the Adige to those of the Piave there stretches, at a variable distance of from three to five miles from the actual shore, a bank of sand, divided into long islands by narrow channels of sea. The space between this bank and the true shore consists of the sedimentary deposits from these and other rivers, a great plain of calcareous mud, covered, in the neighborhood of Venice, by the sea at high water, to the depth in most places of a foot or a foot and a half, and nearly everywhere exposed at low tide, but divided by an intricate network of narrow and winding channels, from which the sea never retires. In some places, according to the run of the currents, the land has risen into marshy islets, consolidated, some by art, and some by time, into ground firm enough to be built upon, or fruitful enough to be cultivated: in others, on the contrary, it has not reached the sea-level; so that, at the average low water, shallow lakelets glitter among its irregularly exposed fields of seaweed. In the midst of the largest of these, increased in importance by the confluence of several large river channels towards one of the openings in the sea bank, the city of Venice itself is built, on a crowded cluster of islands; the various plots of higher ground which appear to the north and south of this central cluster, have at different periods been also thickly inhabited, and now bear, according to their size, the remains of cities, villages, or isolated convents and churches, scattered among spaces of open ground, partly waste and encumbered by ruins, partly under cultivation for the supply of the metropolis.
§ VI. The average rise and fall of the tide is about three feet (varying considerably with the seasons3); but this fall, on so flat a shore, is enough to cause continual movement in the waters, and in the main canals to produce a reflux which frequently runs like a mill stream. At high water no land is visible for many miles to the north or south of Venice, except in the form of small islands crowned with towers or gleaming with villages: there is a channel, some three miles wide, between the city and the mainland, and some mile and a half wide between it and the sandy breakwater called the Lido, which divides the lagoon from the Adriatic, but which is so low as hardly to disturb the impression of the city’s having been built in the midst of the ocean, although the secret of its true position is partly, yet not painfully, betrayed by the clusters of piles set to mark the deep-water channels, which undulate far away in spotty chains like the studded backs of huge sea-snakes, and by the quick glittering of the crisped and crowded waves that flicker and dance before the strong winds upon the unlifted level of the shallow sea. But the scene is widely different at low tide. A fall of eighteen or twenty inches is enough to show ground over the greater part of the lagoon; and at the complete ebb the city is seen standing in the midst of a dark plain of seaweed, of gloomy green, except only where the larger branches of the Brenta and its associated streams converge towards the port of the Lido. Through this salt and sombre plain the gondola and the fishing-boat advance by tortuous channels, seldom more than four or five feet deep, and often so choked with slime that the heavier keels furrow the bottom till their crossing tracks are seen through the clear sea water like the ruts upon a wintry road, and the oar leaves blue gashes upon the ground at every stroke, or is entangled among the thick weed that fringes the banks with the weight of its sullen waves, leaning to and fro upon the uncertain sway of the exhausted tide. The scene is often profoundly oppressive, even at this day, when every plot of higher ground bears some fragment of fair building: but, in order to know what it was once, let the traveller follow in his boat at evening the windings of some unfrequented channel far into the midst of the melancholy plain; let him remove, in his imagination, the brightness of the great city that still extends itself in the distance, and the walls and towers from the islands that are near; and so wait, until the bright investiture and sweet warmth of the sunset are withdrawn from the waters, and the black desert of their shore lies in its nakedness beneath the night, pathless, comfortless, infirm, lost in dark languor and fearful silence, except where the salt runlets plash into the tideless pools, or the sea-birds flit from their margins with a questioning cry; and he will be enabled to enter in some sort into the horror of heart with which this solitude was anciently chosen by man for his habitation. They little thought, who first drove the stakes into the sand, and strewed the ocean reeds for their rest, that their children were to be the princes of that ocean, and their palaces its pride; and yet, in the great natural laws that rule that sorrowful wilderness, let it be remembered what strange preparation had been made for the things which no human imagination could have foretold, and how the whole existence and fortune of the Venetian nation were anticipated or compelled, by the setting of those bars and doors to the rivers and the sea. Had deeper currents divided their islands, hostile navies would again and again have reduced the rising city into servitude; had stronger surges beaten their shores, all the richness and refinement of the Venetian architecture must have been exchanged for the walls and bulwarks of an ordinary sea-port. Had there been no tide, as in other parts of the Mediterranean, the narrow canals of the city would have become noisome, and the marsh in which it was built pestiferous. Had the tide been only a foot or eighteen inches higher in its rise, the water-access to the doors of the palaces would have been impossible: even as it is, there is sometimes a little difficulty,