seldom charged with the construction of works of military defence, but,
like Archimedes at Syracuse, and Longinus at Palmyra, they directed
their attention principally to devising implements of war and the most
effective manner of using them. Engines of war were at that time divided
between the _engigneurs_ and the _artilliers_; the former being charged
with the heavier machines, and the latter with the smaller weapons used
for throwing projectiles. After the invention of gunpowder, the old
battering-rams, cranes, helipoles, &c., disappeared, and with them the
_engigneurs_, or masters of engines. The new inventions were united with
the few old projectile machines that remained in the artillery, and the
engineers were for a time left almost without employment. The revival of
the art of fortification was very slow, and the modern system scarcely
began to be developed till near the sixteenth century.

We must omit for the present giving even an outline of the history of
military engineering, and pass to the troops of this arm, as
constituting an essential element of an army organization. The subject
of fortification, and the history of its various changes, will be
examined in the next chapter.

The engineers, in modern army organization, constitute the fourth arm of
service, as, compared with artillery, their relative numbers are about
as two to three. They are divided in the same manner as the artillery,
viz.:--1st, the staff; 2d, guards, or fort-keepers; 3d, artificers; and
4th, the troops.

I. The officers constituting the staff of this corps are charged in time
of peace with planning, constructing, and repairing all fortifications
and other defensive works; the construction and preparation of all
military materials, and stores connected with this arm; and (in our
service) with the disbursements of money connected with these
operations: in time of war they are charged with the attack and defence
of military works, the laying out and construction of field defences,
redoubts, intrenchments, roads, &c.; in the attack they form a part of
the vanguard, to remove obstructions; and in retreat they form a part
of the rear-guard, to erect obstacles, destroy roads, bridges, &c., so
as to retard an enemy's pursuit.

From the important character of these duties as connected with the means
essential to a national defence, and the vast amount of money expended
in these operations, it is evident that a high order of acquirements