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.
For a long period previous to the Thirty Years' War, its strong castles and fortified cities secured the German empire from attacks from abroad, except on its extensive frontier, which was frequently assailed, but no enemy was able to penetrate to the interior till a want of union among its own princes opened its strongholds to the Swedish conqueror; nor then, did the cautious Gustavus Adolphus venture far into its territories till he had obtained possession of all the military works that might endanger his retreat.
Again, in the Seven Years' War, when the French neglected to secure their foothold in Germany, by placing in a state of defence the fortifications that fell into their power, the first defeat rendered their ground untenable, and threw them from the Elbe back upon the Rhine and the Mayne.

They afterwards took the precaution to fortify their positions, and to secure their magazines under shelter of strong places, and, consequently, were enabled to maintain themselves in the hostile country till the end of the war, notwithstanding the inefficiency of their generals, the great reverses they sustained in the field, the skill and perseverance of the enemy they were contending with, and the weak and vacillating character of the cabinet that directed them.
But this system of defence was not so carefully maintained in the latter part of the eighteenth century, for at the beginning of the French Revolution, says Jomini, "Germany had too few fortifications; they were generally of a poor character, and improperly located." France, on the contrary, was well fortified: and although without armies, and torn in pieces by domestic factions, (we here use the language of the Archduke,) "she sustained herself against all Europe; _and this was because her government, since the reign of Louis XIII_., _had continually labored to put her frontiers into a defensive condition agreeably to the principles of strategy_; starting from such a system for a basis, she subdued every country on the continent that was not thus fortified; and this reason alone will explain how her generals sometimes succeeded in destroying an army, and even an entire state, merely by a strategic success." This may be illustrated by reference to particular campaigns.

In 1792, when the Duke of Brunswick invaded France, she had no armies competent to her defence.