The old system of intrenched camps and lines of contravallation is unsuited to the spirit of modern warfare. In ancient times, and more particularly in the middle ages, too much importance was attached to tactical positions, and not enough to strategic points and lines. This gave to fortifications a character that never properly belonged to them. From the middle ages down to the period of the French Revolution, wars were carried on mainly by the system of positions--one party confining their operations to the security of certain important places, while the other directed their whole attention to the siege and capture of these places. But Carnot and Napoleon changed this system, at the same time with the system of tactics, or rather, returned from it to the old and true system of strategic operations. Some men, looking merely at the fact that a _change_ was made, but without examining the _character_ of that change, have rushed headlong to the conclusion that fortified places are now utterly useless in war, military success depending entirely upon a good system of marches. On this subject, General Jomini, the great military historian of the wars of the French Revolution, remarks that "we should depend entirely upon neither organized masses, nor upon material obstacles, whether natural or artificial. To follow exclusively either of these systems would be equally absurd. The true science of war consists in choosing a just medium between the two extremes. The wars of Napoleon demonstrated the great truth, that distance can protect no country from invasion, but that a state, to be secure, must have a good system of fortresses, and a good system of military reserves and military institutions." In all military operations _time_ is of vast importance. If a single division of an army can be retarded for a few hours only, it not unfrequently decides the fate of the campaign. Had the approach of Blucher been delayed for a few hours, Napoleon must have been victorious at the battle of Waterloo. An equilibrium can seldom be sustained for more than six or seven hours between forces on the field of battle; but in this instance, the state of the ground rendered the movements so slow as to prolong the battle for about twelve hours; thus enabling the allies to effect a concentration in time to save Wellington.