o a deadly cross fire. These intervals also allow
the assailed to act on the offensive, by charging the enemy at the
opportune moment. But with raw and militia forces it will be safer to
resort to continuous lines. If cavalry form any part of the defensive
force, it will be absolutely necessary to leave intervals through which
these troops may charge.

A vertical section of all intrenchments is of the same general form; the
dimensions will, of course, vary with the nature of the soil, and the
time and means employed in their construction. The minimum dimensions
that can be used with any considerable advantage are given in Fig. 49.

In laying out field-works advantage should be taken of all available
artificial obstacles, such as hedges, walls, houses, outbuildings, &c. A
thickset hedge may be rendered defensible by throwing up against it a
slight parapet of earth. Stone fences may be employed in the same way.
Walls of masonry may be pierced with loop-holes and arranged for one or
two tiers of fire. The walls of houses are pierced in the same manner,
and a projecting wooden structure, termed a _machicoulis gallery_, is
sometimes made from the floor of the second story, to enable the
assailed to fire down upon their opponents. This arrangement is
frequently employed to advantage in wooden blockhouses against a savage
foe; but it is of little avail when exposed to the fire of artillery.
Some have proposed galleries of this description in permanent works of
masonry, but the project is too obviously absurd to merit discussion.

In addition to the parapet of an intrenchment, a good engineer will
always find time and means for constructing other artificial obstacles,
such as trous-de-loup, abattis, palisades, stockades, fraises,
chevaux-de-frise, crows'-feet, mines, &c.

_Trous-de-loup_ are pits dug in the earth in the form of an inverted
truncated cone, some six feet in diameter, and about the same number of
feet in depth. They are usually placed a few yards in front of the
ditch, and concealed by some slight covering.

_Abattis_ are tops and large limbs of trees arranged along the glacis of
a work; the ends of the branches are lopped off and sharpened.

_Palisades_ are stakes some eight or ten feet long, with one end
fastened in the ground and the other made sharp. They are placed in
juxtaposition and connected together by horizontal riband-pieces. This
arrangement is frequently placed at the foot of the counterscarp. W