k, but to silence any
artillery the enemy might bring up to batter the bridge while
building. For this purpose it is convenient to have the bank from
which the passage is made somewhat higher than the other.

4. The proximity of a large island near the enemy's bank gives
great facilities for passing over troops in boats and for
constructing the bridge. In like manner, a smaller stream emptying
into the larger near the point of passage is a favorable place for
collecting and concealing boats and materials for the bridge.

5. It is well to choose a position where the river makes a
re-entering bend, as the batteries on the assailant's side can
cross their fire in front of the point where the troops are to land
from the boats and where the end of the bridge is to rest, thus
taking the enemy in front and flank when he attempts to oppose the
passage.

6. The locality selected should be near good roads on both banks,
that the army may have good communications to the front and rear on
both banks of the river. For this reason, those points where the
banks are high and steep should be usually avoided.

The rules for preventing a passage follow as a matter of course from
those for effecting it, as the duty of the defenders is to counteract
the efforts of the assailants. The important thing is to have the
course of the river watched by bodies of light troops, without
attempting to make a defense at every point. Concentrate rapidly at the
threatened point, in order to overwhelm the enemy while a part only of
his army shall have passed. Imitate the Duke of Vendome at Cassano, and
the Archduke Charles at Essling in 1809,--the last example being
particularly worthy of praise, although the operation was not so
decidedly successful as might have been expected.

In Article XXI. attention was called to the influence that the passage
of a river, in the opening of a campaign, may have in giving direction
to the lines of operations. We will now see what connection it may have
with subsequent strategic movements.

One of the greatest difficulties to be encountered after a passage is to
cover the bridge against the enemy's efforts to destroy it, without
interfering too much with the free movement of the army. When the army
is numerically very superior to the enemy, or when the river is passed
just after a great victory gained, the difficulty mentione