h Africa for connecting lines between blockhouses.
When used in this way the lines of fence may be 300 to 600 yds. long,
in plan like a worm fence, with the blockhouse at the reentrant
angles. Fixed rests for rifles, giving them the proper aim to enfilade
the fence, were prepared at the blockhouses for use at night.

[Illustration: Fig. 13]

[Illustration: Fig. 14]

Such a fence may be arranged in many ways to give an automatic alarm
either mechanically or electrically. The mechanical forms mostly
depend on one or more single wires which are smooth, and are tightly
stretched through staples on the posts which hold them loosely,
permitting them to slip when cut and drop a counterweight at the
blockhouse, which in falling explodes a cap or pulls the trigger of a
rifle.

=1184. Military pits= or =trous de loup= are excavations in the shape
of an inverted cone or pyramid, with a pointed stake in the bottom.
They should not be so deep as to afford cover to the skirmisher. Two
and one-half feet or less is a suitable depth. Fig. 15 shows a plan
and section of such pits.

[Illustration: Fig. 15]

They are usually dug in 3 or 5 rows and the earth thrown to the front
to form a glacis. The rear row is dug first and then the next in
front, and so on, so that no earth is cast over the finished pits.

An excellent arrangement is to dig the pits in a checkerboard plan,
leaving alternate squares and placing a stake in each of them to form
a wire entanglement, Fig. 16. One man can make 5 pits on a 2-hour
relief.

[Illustration: Fig. 16]

=1185. Miscellaneous barricades.= Anything rigid in form and movable
may be used to give cover from view and fire and to obstruct the
advance of an assailant. Boxes, bales and sacks of goods, furniture,
books, etc., have been so used. The principles above stated for other
obstacles should be followed, so far as the character of the materials
will permit. The rest ingenuity must supply. Such devices are usually
called barricades and are useful in blocking the streets of towns and
cities.

=1186. Inundations.= Backing up the water of a stream so that it
overflows a considerable area forms a good obstacle even though of
fordable depth. If shallow, the difficulty of fording may be increased
by irregular holes or ditches dug before the water comes up or by
driving stakes or making entanglements. Fords have frequently been
obstructed by ordinary harrows laid on the bottom with the teeth up.

T