temporary lines of defence.

It will be seen from these remarks that lines of defence are not
necessarily bases of operation.

_Strategic positions_ are such as are taken up during the operations of
a war, either by a _corps d'armée_ or grand detachment, for the purpose
of checking or observing an opposing force; they are named thus to
distinguish them from tactical positions or fields of battle. The
positions of Napoleon at Rivoli, Verona, and Legnano, in 1796 and 1797,
to watch the Adige; his positions on the Passarge, in 1807, and in
Saxony and Silesia in front of his line of defence, in 1813; and
Massena's positions on the Albis, along the Limmat and the Aar, in 1799,
are examples under this head.

Before proceeding further it may be well to illustrate the strategic
relations of lines and positions by the use of diagrams.

(Fig. 1.) The army at A covers the whole of the ground in rear of the
line DC perpendicular to the line AB, the position of the enemy being at
B.

(Fig. 2.) AJ being equal to BJ, A will still cover every thing in rear
of DC.

(Fig. 3.) If the army A is obliged to cover the point _a_, the army B
will cover all the space without the circle whose radius is _a_ B; and of
course A continues to cover the point _a_ so long as it remains within
this circle _a_ B.