An army which undertakes the conquest of a country, has its two wings resting either upon neutral territories, or upon great natural obstacles, such as rivers or chains of mountains. It happens in some cases that only one wing is so supported; and in others that both are exposed.

In the first instance cited, viz., where both wings are protected, a general has only to protect his front from being penetrated. In the second, where one wing only is supported, he should rest upon the supported wing. In the third, where both wings are exposed, he should depend upon a central formation, and never allow the different corps under his command to depart from this: for if it be difficult to contend with the disadvantage of having two flanks exposed, the inconvenience is doubled by having four, trebled if there be six—that is to say, if the army is divided into two or three different corps. In the first instance, then, as above quoted, the line of operation may rest indifferently on the right or on the left. In the second, it should be directed toward the wing in support. In the third, it should be perpendicular to the centre of the army’s line of march. But in all these cases it is necessary, at a distance of every five or six days march, to have a strong post or an entrenched position upon the line of operation, in order to collect military stores and provisions, to organize convoys, to form of it a centre of movement, and establish a point of defence to shorten the line of operation of the army.