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.