With respect to both forms of defence of large and small rivers, we must observe generally, that if they are undertaken in the haste and confusion of a retreat, without preparation, without the removal of all means of passage, and without an exact knowledge of the country, they cannot certainly fulfil what has been here supposed; in most such cases, nothing of the kind is to be calculated upon; and therefore it will be always a great error for an army to divide itself over extended positions.
As everything usually miscarries in war, if it is not done upon clear convictions and with the whole will and energy, so a river defence will generally end badly when it is only resorted to because we have not the heart to meet the enemy in the open field, and hope that the broad river or the deep valley will stop him. When that is the case, there is so little confidence in the actual situation that both the general and his army are usually filled with anxious forebodings, which are almost sure to be realized quick enough. A battle in the open field does not suppose a perfectly equal state of circumstances beforehand, like a duel; and the defender who does not know how to gain for himself any advantages, either through the special nature of the defence, through rapid marches, or by knowledge of the country and freedom of movement, is one whom nothing can save, and least of all will a river or its valley be able to help him.
The third form of defence—by a strong position taken up on the enemy’s side of the river—founds its efficacy on the danger in which it places the enemy of having his communications cut by the river, and being thus limited to some bridges. It follows, as a matter of course, that we are only speaking of great rivers with a great volume of water, as these alone can lead to such results, whilst a river which is merely in a deep ravine usually affords such a number of passages that all danger of the above disappears.
But the position of the defensive must be very strong, almost unassailable; otherwise he would just meet the enemy half way, and give