"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. 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.