Trieste and Venice, though for the moment they empty themselves
and their store of detritus into the open Adriatic.

Fix your eyes for a moment on Venetia proper, and you will see how this
has all happened and is still happening. Each mountain torrent that
leaps from the Tyrolese Alps bring down in its lap a rich mass of mud,
which has gradually spread over a strip of sea some forty or fifty
miles wide, from the base of the mountains to the modern coast-line of
the province. Near the sea--or, in other words, at the temporary
outlet--it forms banks and lagoons, of which those about Venice are the
best known to tourists, though the least characteristic. For miles and
miles between Venice and Trieste the shifting north shore of the
Adriatic consists of nothing but such accumulating mud banks. Year
after year they push farther seaward, and year after year fresh islets
and shoals grow out into the waves beyond the temporary deltas. In
time, therefore, the gathering mud banks of these Alpine torrents must
join the greater mud bank that runs rapidly seaward at the delta of the
Po. As soon as they do so the rivers must rush together, and what was
once an independent stream, emptying itself into the Adriatic, must
become a tributary of the Po, helping to swell the waters of that great
united river. The Adige has now just reached this state: its delta is
continuous with the delta of the Po, and their branches interosculate.
The Mincio and the Adda reached it ages since: the Piave and the
Livenia will not reach it for ages. In Roman days Hatria was still on
the sea: it is now some fifteen miles inland.

From all this you can gather why the existing Po flows far from the
Alps and nearer the base of the Apennines. The Alpine streams in far
distant days brought down relatively large floods of glacial mud;
formed relatively large deltas in the old Lombard bay; filled up with
relative rapidity their larger half of the basin. The Apennines, less
lofty, and free from glaciers, sent down shorter and smaller torrents,
laden with far less mud, and capable therefore of doing but little
alluvial work for the filling in of the future Lombardy. So the river
was pushed southward by the Alpine deposits of the northern streams,
leaving the great plains of Cisalpine Gaul spread away to the north of
it.

And this land-making action is ceaseless and continuous. About Venice,
Chioggia, Maestra, Comacchio, the delta of the Po is still spreading
seaw