st of books of reference on Military
Engineering will be given at the close of the following chapters.

While these pages are passing through the press, Congress has authorized
the President to raise _one company_ of engineer troops! This number is
altogether too small to be of any use in time of war.]

CHAPTER XIII.

PERMANENT FORTIFICATIONS.

_Fortification_ is defined,--the art of disposing the ground in such a
manner as to enable a small number of troops to resist a larger army the
longest time possible. If the work be placed in a position of much
importance, and its materials be of a durable character, it is called
permanent; if otherwise, it receives the appellation of _field_, or
_temporary_. Fieldworks are properly confined to operations of a single
campaign, and are used to strengthen positions which are to be occupied
only for a short period. Generally these works are of earth, thrown up
by the troops in a single day. They are intimately connected with a
system of permanent fortifications, but from the facility of their
construction, no provision need be made for them before the actual
breaking out of war. Indeed, they could not well be built before
hostilities commenced, as their locality in each case must be determined
by the position of the hostile forces.

Having already described the general influence of permanent
fortifications as a means of national defence, we shall here speak
merely of the principles of their construction. It is not proposed to
enter into any technical discussion of matters that especially belong
to the instruction of the engineer, but merely to give the nomenclature
and use of the more important parts of a military work; in a word, such
general information as should belong to officers of every grade and
corps of an army.

The first species of fortification among the ancients was of course very
simple, consisting merely of an earthen mound, or palisades. A wall was
afterwards used, and a ditch was then added to the wall. It was found
that a straight wall could be easily breached by the enemy's
battering-rams; to remedy this evil, towers were built at short
intervals from each other, forming a broken line of salient and
re-entering parts. These towers or salient points gradually assumed a
shape approximating to the modern bastion.

After the invention of gunpowder and the application of cannon to the
attack and defence of places, it became necessary to arrange earthen