_Defence of Intervals of Forts._--The frontal fire of the batteries in
the intervals and the flanking fire of some of the guns in the forts
will play an important part, but the main reliance should be on
infantry defence. A fully prepared fortress would have practically a
complete chain of infantry fighting positions and obstacles between
the forts, at all events on the fronts likely to be seriously
attacked. The positions would consist largely of fire trenches, with
good communications; but it is pretty generally recognized that there
must be some _points d'appui_ in the shape of redoubts or infantry
forts, and also bomb-proof shelter for men, ammunition and stores near
the fighting line. This is usually included in the redoubts. If they
are to resist the heaviest shell, such shelters must be built in peace
time.
_Communications_ are of the first importance, not merely to facilitate
the movement of the enormous stores of ammunition and materials
required in the fighting line, but also that defenders may fully
utilize the advantage of acting on interior lines. They should include
both railways and roads running from the centre of the place to the
different sectors of defence, and all round, in rear of the line of
forts; also ample covered approaches to the fighting line. Concealment
is essential, and where the lie of the ground does not help, it must
be got from earth parapets or plantations.
Barrier forts.
The principal use of barrier forts is in country where the necessary
line of communication cannot be easily diverted. For instance, in a
comparatively flat country a barrier fort commanding a road or railway
is of little use because roads may be found passing round it, or a line
of railway may be diverted for some miles to avoid it. But in
mountainous country, where such diversion is impossible, it will be
necessary for the enemy to capture the fort before he can advance; and
the impossibility of surrounding it, the few positions from which siege
artillery can be brought into play, and the fact that there is
practically only one road of approach to be denied, make these positions
peculiarly suitable for forts with armoured batteries. Italy makes
considerable use of such forts for the defence of frontier passes.
_General Brialmont's Theoretical Claim for the Defence of a
Country._--Before going into details, it is worth while to state the
full claim of strategic fortification advanced by General Brialmont,
the most thorough of all its advocates. It is as follows:--
A. Fortify the capital.
B. Fortify the points where main lines of communication pass a
strategic barrier.
C. Make an entrenched camp at the most important centre of
communication in each zone of invasion: and support it by one or two
places arranged so as to make a fortified district.
[Illustration: From Brialmont's _Progres de la defense des etats et de
la fortification depuis Vauban_, by permission of Commandant G. Meeus.