"Fortifications," says Jomini, "fulfil two objects of capital
importance,--1st. The protection of the frontiers; and 2d. Assisting the
operations of the army in the field." "Every part of the frontiers of a
state should be secured by one or two great places of refuge, secondary
places, and even small posts for facilitating the active operations of
the armies. Cities girt with walls and slight ditches may often be of
great utility in the interior of a country, as places of deposit, where
stores, magazines, hospitals, &c., may be sheltered from the incursions
of the enemy's light troops. These works are more especially valuable
where such stores, in order not to weaken the regular army by
detachments, are intrusted to the care of raw and militia forces." It is
not supposed that any system of fortifications can hermetically close a
frontier; "but, although they of themselves can rarely present an
absolute obstacle to the advance of the hostile army, yet it is
indisputable that they straiten its movements, change the direction of
its marches, and force it into detachments; while, on the contrary, they
afford all the opposite advantages to the defensive army; they protect
its marches, favor its debouches, cover its magazines, its flanks, and
its movements, and finally furnish it with a place of refuge in time of
need."

These opinions were uttered, be it remembered, long since the period at
which modern military quacks date the downfall of fortifications as
inland defences, by men, too, who were not engineers, and consequently
had no professional predilections in favor of fortifications. The
Archduke Charles, as a general, knew no rival but Napoleon, and General
Jomini is universally regarded as the first military historian of the
age. The truth of their remarks on fortifications is most fully
confirmed by the military histories of Germany and France.