a, are not so formidable that they cannot be made more so by a
good system of fortresses.

Of all these frontiers, that separating France and Piedmont was best
covered. The valleys of the Stura and Suza, the passes of Argentine, of
Mont-Genevre, and of Mont-Cenis,--the only ones considered
practicable,--were covered by masonry forts; and, in addition, works of
considerable magnitude guarded the issues of the valleys in the plains
of Piedmont. It was certainly no easy matter to surmount these
difficulties.

These excellent artificial defenses will not always prevent the passage
of an army, because the small works which are found in the gorges may be
carried, or the enemy, if he be bold, may find a passage over some other
route hitherto deemed impracticable. The passage of the Alps by Francis
I.,--which is so well described by Gaillard,--Napoleon's passage of the
Saint-Bernard, and the Splugen expedition, prove that there is truth in
the remark of Napoleon, _that an army can pass wherever a titan can set
his foot_,--a maxim not strictly true, but characteristic of the man,
and applied by him with great success.

Other countries are covered by large rivers, either as a first line or
as a second. It is, however, remarkable that such lines, apparently so
well calculated to separate nations without interfering with trade and
communication, are generally not part of the real frontier. It cannot be
said that the Danube divides Bessarabia from the Ottoman empire as long
as the Turks have a foothold in Moldavia. The Rhine was never the real
frontier of France and Germany; for the French for long periods held
points upon the right bank, while the Germans were in possession of
Mayence, Luxembourg, and the _tetes de ponts_ of Manheim and Wesel on
the left bank.

If, however, the Danube, the Rhine, Rhone, Elbe, Oder, Vistula, Po, and
Adige be not exterior lines of the frontier, there is no reason why they
should not be fortified as lines of permanent defense, wherever they
permit the use of a system suitable for covering a front of operations.

An example of this kind is the Inn, which separates Bavaria from
Austria: flanked on the south by the Tyrolese Alps, on the north by
Bohemia and the Danube, its narrow front is covered by the three
fortified places of Passau, Braunau, and Salzburg. Lloyd, with some
poetic license, compares this frontier to two impregnable bastions whose
curtain is formed of three fine forts and whose ditc