century; and Dante, writing in the beginning of
the fourteenth, describes, in the seventh circle of hell, a rivulet of
tears separated from a burning sandy desert by embankments "like those
which, between Ghent and Bruges, were raised against the ocean, or those
which the Paduans had erected along the Brenta to defend their villas on
the melting of the Alpine snows."

Quale i Fiamminghi tra Guzzante e Bruggia,
Temendo il fiotto che in ver lor s'avventa,
Fanno lo schermo, perche il mar si fuggia,
E quale i Padovan lungo la Brenta,
Per difender lor ville e lor castelli,
Anzi che Chiarentana il caldo senta.--

_Inferno_, Canto xv.

In the Adriatic, from the northern part of the Gulf of Trieste, where
the Isonzo enters, down to the south of Ravenna, there is an
uninterrupted series of recent accessions of land, more than 100 miles
in length, which, within the last 2000 years, have increased from _two
to twenty miles in breadth_. A line of sand-bars of great length has
been formed nearly all along the western coast of this gulf, inside of
which are lagunes, such as those of Venice, and the large lagune of
Comacchio, 20 miles in diameter. Newly deposited mud brought down by the
streams is continually lessening the depth of the lagunes, and
converting part of them into meadows.[340] The Isonzo, Tagliamento,
Piave, Brenta, Adige, and Po, besides many other inferior rivers,
contribute to this advance of the coast-line and to the shallowing of
the lagunes and the gulf.

_Delta of the Po._--The Po and the Adige may now be considered as
entering by one common delta, for two branches of the Adige are
connected with arms of the Po, and thus the principal delta has been
pushed out beyond those bars which separate the lagunes from the sea.
The rate of the advance of this new land has been accelerated, as before
stated, since the system of embanking the rivers became general,
especially at that point where the Po and Adige enter. The waters are no
longer permitted to spread themselves far and wide over the plains, and
to leave behind them the larger portion of their sediment. Mountain
torrents also have become more turbid since the clearing away of
forests, which once clothed the southern flanks of the Alps. It is
calculated that the mean rate of advance of the delta of the Po on the
Adriatic between the years 1200 and 1600 was 25 yards or metres a year,
whereas the mean annual gain from 1600 to 1804 was 70 metr