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.