objects is more dangerous than the diversions above referred to, it is
no less true that they are often highly proper and, it may be,
indispensable.

These great detachments are chiefly of two kinds. The first are
permanent corps which must be sometimes thrown out in a direction
opposite to the main line of operations, and are to remain throughout a
campaign. The second are corps temporarily detached for the purpose of
assisting in carrying out some special enterprise.

Among the first should be especially enumerated those fractions of an
army that are detached either to form the strategic reserve, of which
mention has been made, or to cover lines of operation and retreat when
the configuration of the theater of the war exposes them to attack. For
example, a Russian army that wishes to cross the Balkan is obliged to
leave a portion of its forces to observe Shumla, Routchouk, and the
valley of the Danube, whose direction is perpendicular to its line of
operations. However successful it may be, a respectable force must
always be left toward Giurgevo or Krajova, and even on the right bank of
the river toward Routchouk.

This single example shows that it is sometimes necessary to have a
double strategic front, and then the detachment of a considerable corps
must be made to offer front to a part of the enemy's army in rear of the
main army. Other localities and other circumstances might be mentioned
where this measure would be equally essential to safety. One case is the
double strategic front of the Tyrol and the Frioul for a French army
passing the Adige. On whichever side it may wish to direct its main
column, a detachment must be left on the other front sufficiently strong
to hold in check the enemy threatening to cut the line of
communications. The third example is the frontier of Spain, which
enables the Spaniards to establish a double front,--one covering the
road to Madrid, the other having Saragossa or Galicia as a base. To
whichever side the invading army turns, a detachment must be left on the
other proportioned in magnitude to the enemy's force in that direction.

All that can be said on this point is that it is advantageous to enlarge
as much as possible the field of operations of such detachments, and to
give them as much power of mobility as possible, in order to enable them
by opportune movements to strike important blows. A most remarkable
illustration of this truth was given by Napoleon in the campaign o