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.