ctive armies are of
two kinds. An invading army may pass by fortified places without
attacking them, but it must leave a force to invest them, or at least to
watch them; and when there are a number of them adjacent to each other
it will be necessary to leave an entire corps d'armee, under a single
commander, to invest or watch them as circumstances may require. When
the invading army decides to attack a place, a sufficient force to carry
on the siege will be assigned to this duty; the remainder may either
continue its march or take a position to cover the siege.

Formerly the false system prevailed of encircling a city by a whole
army, which buried itself in lines of circumvallation and
contravallation. These lines cost as much in labor and expense as the
siege itself. The famous case of the lines of Turin, which were fifteen
miles in length, and, though guarded by seventy-eight thousand French,
were forced by Prince Eugene with forty thousand men in 1706, is enough
to condemn this ridiculous system.

Much as the recital of the immense labors of Caesar in the investment of
Alise may excite our admiration, it is not probable that any general in
our times will imitate his example. Nevertheless, it is very necessary
for the investing force to strengthen its position by detached works
commanding the routes by which the garrison might issue or by which the
siege might be disturbed from without. This was done by Napoleon at
Mantua, and by the Russians at Varna.

Experience has proved that the best way to cover a siege is to beat and
pursue as far as possible the enemy's forces which could interfere. If
the besieging force is numerically inferior, it should take up a
strategic position covering all the avenues by which succor might
arrive; and when it approaches, as much of the besieging force as can be
spared should unite with the covering force to fall upon the approaching
army and decide whether the siege shall continue or not.

Bonaparte in 1796, at Mantua, was a model of wisdom and skill for the
operations of an army of observation.

INTRENCHED LINES.

Besides the lines of circumvallation and contravallation referred to
above, there is another kind, which is more extended than they are, and
is in a measure allied to permanent fortifications, because it is
intended to protect a part of the frontiers.

As a fortress or an intrenched camp may, as a temporary refuge for an
army, be highly advantageous, so to the sam