the Chickahominy in the
Peninsular campaign. 'Sumner's bridge,' by which reinforcements crossed
at the battle of Fair Oaks, was laid in this manner. Of course such
bridges are liable to be carried away and to be easily destroyed. Some
of the bridges over the Chickahominy were laid much more thoroughly.
'Cribs' of logs were piled in cob-house fashion, pinned together, and
sunk vertically in the stream. Then string pieces and the flooring were
laid, the whole covered with brush and dirt. Men worked at these bridges
up to the waist in water for many days in succession.

Military art has devised many expedients for bridging streams, and use
is made of any facilities that may be at hand for constructing the means
of passage; but the only organized bridge trains which move with the
army are those which carry the pontoons. Of these there are various
kinds, made of wood, of corrugated iron, and of india rubber stretched
over frames. But the wooden pontoon boats are most in use. They can be
placed in a river and the flooring laid upon them with great rapidity.
Several very fine bridges have been thus constructed--among them may be
mentioned the one at the mouth of the Chickahominy, across which General
McClellan's army marched in retreating from Harrison's Landing. It was
about a mile long, and was constructed in a few hours.

To cross a river under the fire of an enemy is one of the most difficult
operations in warfare. Yet it has been frequently accomplished by our
armies. The crossing of the Rappahannock by General Burnside's army,
previous to the great battle of Fredericksburg, in December, 1862, is
one of the most remarkable instances of the kind during the war. The
rebel rifle pits lined the southern bank, and the fire from them
prevented our engineers from approaching--the river being only about
seventy-five yards wide. For a long time our artillery failed to drive
the rebels away. About noon of the day on which the crossing was made,
General Burnside ordered a concentration of fire on Fredericksburg, in
the houses of which place the rebels had concealed their forces. A
hundred guns, hurling shot and shell into every building and street of
the city, soon riddled it; but the obstinate foes hid themselves in the
cellars till the storm was over, and then emerged defiantly. They were
only dislodged by sending over a battalion in boats to attack them in
flank, when they retreated, and the bridges were laid.

It is impossible