A small body, even when the forces on both sides are equal can never make as long a stand as a considerable corps; for the larger the masses the more time they require to complete their action, of whatever kind it may be. In a mountainous country the mere marching is of itself slower, the resistance in the different positions longer, and attended with less danger, and at every step favourable positions may be found.
As the distance to which a corps is pushed forward increases so will the length of its retreat, and therefore also the absolute gain of time by its resistance; but as such a corps by its position has less power of resistance in itself, and is less easily reinforced, its retreat must be made more rapidly in proportion than if it stood nearer the main body, and had a shorter distance to traverse.
The support and means of rallying afforded to an advanced corps must naturally have an influence on the duration of the resistance, as all the time that prudence requires for the security of the retreat is so much taken from the resistance, and therefore diminishes its amount.
There is a marked difference in the time gained by the resistance of an advanced corps when the enemy makes his first appearance after midday; in such a case the length of the night is so much additional time gained, as the advance is seldom continued throughout the night. Thus it was that, in 1815, on the short distance from Charleroi to Ligny, not more than two miles,(*) the first Prussian corps under General Ziethen, about 30,000 strong, against Buonaparte at the head of 120,000 men, was enabled to gain twenty-four hours for the Prussian army then engaged in concentrating. The first attack was made on General Ziethen about nine o’clock on the morning of 15th June, and the battle of Ligny did not commence until about two on the afternoon of 16th. General Ziethen suffered, it is true, very considerable loss, amounting to five or six thousand men killed, wounded or prisoners.