NOTE.
The brilliant success of the allied armies in the campaign of 1814, has given to many military men a false idea of the real value of fortresses.
The formidable bodies which crossed the Rhine and the Alps at this period, were enabled to spare large detachments to blockade the strong places that covered the frontiers of France, without materially affecting the numerical superiority of the army which marched upon the capital. This army was in a condition, therefore, to act, without the fear of being menaced in its line of retreat.
But at no period of military history were the armies of Europe so combined before, or governed so entirely by one common mind in the attainment of a single object. Under these circumstances, the line of fortresses which surround France was rendered unavailable during the campaign; but it would be very imprudent, therefore, to conclude that a frontier guarded by numerous fortresses may be passed with impunity; or that battles may be fought with these places in your rear, without previously besieging, or at least investing them with sufficient forces.
MAXIM XLI.
There are only two ways of insuring the success of a siege. The first, to begin by beating the enemy’s army employed to cover the place, forcing it out of the field, and throwing its remains beyond some great natural obstacle, such as a chain of mountains, or large river. Having accomplished this object, an army of observation should be placed behind the natural obstacle, until the trenches are finished and the place taken.
But if it be desired to take the place in presence of a relieving army, without risking a battle, then the whole materiel and equipment for a siege are necessary to begin with, together with ammunition and provisions for the presumed period of its duration, and also lines of contravallation and circumvallation, aided by all the localities of heights, woods, marshes and inundations.
Having no longer occasion to keep up communications with your depôts, it is now only requisite to hold in check the relieving army. For this purpose, an army of observation should be formed, whose business it is never to lose sight of that of the enemy, and which, while it effectually bars all access to the place, has always time enough to arrive upon his flanks or rear in case he should attempt to steal a march.
It is to be remembered, too, that by profiting judiciously by the lines of contravallation, a portion of the besieging army will always be available in giving battle to the approaching enemy.
Upon the same general principle, when a place is to be besieged in presence of an enemy’s army, it is necessary to cover the siege by lines of circumvallation.
If the besieging force is of numerical strength enough (after leaving a corps before the place four times the amount of the garrison) to cope with the relieving army, it may remove more than one day’s march from the place; but if it be inferior in numbers after providing for the siege, as above stated, it should remain only a short day’s march from the spot, in order to fall back upon its lines, if necessary, or receive succor in case of attack.
If the investing corps and army of observation are only equal when united to the relieving force, the besieging army should remain entire within, or near its lines, and push the works and the siege with the greatest activity.