ith
naval descents upon our maritime cities.

The first point to be attended to in a plan of military operation is to
select a good _base_. Many circumstances influence this selection, such
as mountains, rivers, roads, forests, cities, fortifications, military
depots, means of subsistence, &c. If the frontier of a state contain
strong natural or artificial barriers, it may serve not only as a good
base for offensive operations, but also as an excellent line of defence
against invasion. A single frontier line may, however, be penetrated by
the enemy, and in that case a second or third base further in the
interior becomes indispensable for a good defence.

A French army carrying on military operations against Germany would make
the Rhine its first base; but if driven from this it would form a second
base on the Meuse or Moselle, a third on the Seine, and a fourth on the
Loire; or, when driven from the first base, it would take others
perpendicular to the front of defence, either to the right, on Befort
and Besancon, or to the left, on Mezieres and Sedan. If acting
offensively against Prussia and Russia, the Rhine and the Main would
form the first base the Elbe and the Oder the second, the Vistula the
third, the Nieman the fourth, and the Dwina and the Dnieper the fifth.

A French army operating against Spain would have the Pyrenees for its
first base; the line of the Ebro for a second, resting its wings on the
gulf of Gascony and the Mediterranean. If from this position it advance
its left, possessing itself of the kingdom of Valencia, the line of the
Sierra d'Estellas becomes its third base of operations against the
centre of Spain.

A base may be parallel, oblique, or perpendicular to our line of
operations, or to the enemy's line of defence. Some prefer one plan and
some another; the best authorities, however, think the oblique or
perpendicular more advantageous than the parallel; but we are not often
at liberty to choose between these, for other considerations usually
determine the selection.

In 1806, the French forces first moved perpendicular to their base on
the Main, but afterwards effected a change of front, and moved on a line
oblique or nearly parallel to this base. They had pursued the same plan
of operations in the Seven Years' War. The Russians, in 1812, based
perpendicularly on the Oka and the Kalouga, and extended their flank
march on Wiozma and Krasnoi; in 1813, the allies, based perpendicularly
on