In considering the history of siegecraft since the introduction of
gunpowder, there are three main lines of development to follow, viz. the
gradually increasing power of artillery, the systematizing of the works
of attack, and in recent times the change that has been brought about by
the effect of modern small-arm fire.
Cannon appear to have been first used in sieges as mortars, to destroy
hoardings by throwing round stones and barrels of burning composition.
Early in the 15th century we find cannon throwing metal balls, not only
against hoarding and battlements, but also to breach the bases of the
walls. It was only possible to work the guns very slowly, and archers or
crossbowmen were needed in support of them, to drive the defenders from
the crenellations or loopholes of the battlements. At that period the
artillery was used in place of the medieval siege engines and in much
the same manner. The guns of the defence were inaccurate, and being
placed high on the walls were made ineffective by bad mountings, which
did not allow of proper depression. The besieger therefore could place
his guns close to the walls, with only the protection of a few large
gabions filled with earth, set up on the ground on either side of the
muzzle.
In the course of the 15th century the power of artillery was largely
increased, so that walls and gates were destroyed by it in an
astonishingly short time. Three results shortly followed. The guns of
the defence having gained equally in effectiveness, greater protection
was needed for the attack batteries; bastions and outworks were
introduced to keep the besieger at a distance from the inner walls; and
the walls were sunk in ditches so that they could only be breached by
batteries placed on the edge of the glacis.
Early in the 16th century fortresses were being rapidly remodelled on
these lines, and the difficulties of the attack were at once very much
increased. The tendency of the assailants was still to make for the
curtain, which had always been considered the weak point; but the
besiegers now found that they had to bring their guns right up to the
edge of the ditch before they could make a breach, and in doing so had
to pass over ground which was covered by the converging fire from the
faces of the bastions. Towards the end of the century the attack of the
curtain was delayed and the cross-fire over the ground in front
increased by the introduction of ravelins.
The slight gabion protection for the siege batteries was at first
replaced by strong timber shelters. These were found inadequate; but a
still greater difficulty was that of bringing up the siege guns to their
positions, emplacing them and maintaining communication with them under
fire. In addition to this, the guns of the defence until they could be
overpowered (a slow process) dominated a wide belt of ground in front of
the fortress; and unless the besiegers could find some means of
maintaining a strong guard close to their batteries these were liable to
be destroyed by sorties from the covered way.
Siegecraft before Vauban.
Gradually the whole problem of siege work centred round the artillery.
The besiegers found that they had first to bring up enough guns to
overpower those of the defence; then to advance their guns to positions
from which they could breach the walls; and throughout these operations
to protect them against sorties. Breaches once made, the assault could
follow on the old lines.
The natural solution of the difficulty of approach to the battery
positions was the use of trenches. The Turks were the first to make
systematic use of them, having probably inherited the idea from the
Eastern Empire. The soldiers of Christendom, however, strongly disliked
digging, and at first great leaders like Bayard and Montluc had
themselves to use pick and shovel, to give their men an example. In due
course the necessity of the trenches was recognized, but the soldiers
never took kindly to them, and the difficulty was dealt with in a manner
reminiscent of the feudal ages, by impressing large bodies of peasantry
as workmen whenever a siege was in contemplation.
Through the 16th and most of the 17th century, therefore, we find the
attack being conducted by means of trenches leading to the batteries,
and supported by redoubts often called "places of arms" also made by
trench work. During this period the result of a siege was always
doubtful. Both trenches and batteries were arranged more or less at
haphazard without any definite plan; and naturally it often happened
that offensive action by the besieged against the trenches would
disorder the attack and at times delay it indefinitely. Fig. 64, taken
from a late 17th-century print by de Fer of Paris, gives a good idea of
the general practice of that day when Vauban's methods were not yet
generally known.
Another weak point about the attack was that after the escarp walls had
been strengthened to resist artillery fire as has been described, there
was no clear idea as to how they should be breached. The usual process
was merely an indiscriminate pounding from batteries established on the
crest of the glacis. Thus there were cases of sieges being abandoned
after they had been carried as far as the attempt to breach.
It is in no way strange that this want of method should have
characterized the attack for two centuries after artillery had begun to
assert its power. At the outset many new ideas had to be assimilated.
Guns were gradually growing in power; sieges were conducted under all
sorts of conditions, sometimes against medieval castles, sometimes
against various and widely-differing examples of the new fortification;
and the military systems of the time were not favourable to the
evolution of method. It is the special feature of Vauban's practical
genius for siege warfare that he introduced order into this chaos and
made the issue of a siege under normal conditions, a mere matter of
time, usually a very short time.
Vauban's teaching.
The whole of Vauban's teaching and practice cannot be condensed into the
limits of this article, but special reference must be made to several
points. The most important of these is his general arrangement of the
attack. The ultimate object of the attack works was to make a breach for
the assaulting columns. To do this it was necessary to establish
breaching batteries on the crest of the glacis; and before this could be
done it was necessary to overpower the enemy's artillery. This
preliminary operation is nowadays called the "artillery duel." In
Vauban's day the effective range of guns was 600 to 700 yds. He tells us
that it was customary to establish batteries at 1000 yds. from the
place, but that at that range they did little more than make a great
deal of noise. The first object of the attack, therefore, after the
preliminary operations of investment, &c., had been completed, was to
establish batteries within 600 or 700 yds. of the place, to
counter-batter or enfilade all the faces bearing on the front of attack;
and to protect these batteries against sorties. After the artillery of
the defences had been subdued--if it could not be absolutely
silenced--it was necessary to push trenches to the front so that guns
might be conveyed to the breaching positions and emplaced there in
batteries. Throughout these processes it was necessary to protect the
working parties and the batteries against sorties.
[Illustration: FIG. 64.--Siege-works of the 17th century.]
For this purpose Vauban devised the _Places d'armes_ or _lignes
paralleles_. He tells us that they were first used in 1673 at the siege
of Maestricht, where he conducted the attack, and which was captured in
thirteen days after the opening of the trenches. The object of these
parallels was to provide successive positions for the guard of the
trenches, where they could be at hand to repel sorties. The latter were
most commonly directed against the trenches and batteries, to destroy
them and drive out the working parties. The most vulnerable points were
the heads of the approach trenches. It was necessary, therefore, that
the guard of the trenches should be in a position to reach the heads of
the approaches more quickly than the besieged could do so from the
covered way. This was provided for as follows.
The first parallel was usually established at about 600 yds. from the
place, this being considered the limiting range of action of a sortie.
The parallel was a trench 12 to 15 ft. wide and 3 ft. deep, the
excavated earth being thrown forward to make a parapet 3 or 4 ft. high.
In front of the first parallel and close to it were placed the batteries
of the "first artillery position."
The attack.
While these batteries were engaged in silencing the enemy's artillery,
for which purpose most of them were placed in prolongation of the faces
of the fortress so as to enfilade them, the "Approach Trenches" were
being pushed forward. The normal attack included a couple of bastions
and the ravelin between, with such faces of the fortress as could
support them; and the approach trenches (usually three sets) were
directed on the capitals of the bastions and ravelin, advancing in a
zigzag so arranged that the prolongations of the trenches always fell
clear of the fortress and could not be enfiladed.
Fig. 65, taken from Vauban's _Attack and Defence of Places_, shows
clearly the arrangement of trenches and batteries.
After the approach trenches had been carried forward nearly half-way
to the most advanced points of the covered way, the "second parallel"
was constructed, and again the approach trenches were pushed forward.
Midway between the second parallel and the covered way, short branches
called _Demi-parallels_ were thrown out to either flank of the
attacks: and finally at the foot of the glacis came the third
parallel. Thus there was always a secure position for a sufficient
guard of the trenches. Upon an alarm the working parties could fall
back and the guard would advance.
Trenches were either made by _common trenchwork, flying trenchwork or
sap_. In the first two a considerable length of trench was excavated
at one time by a large working party extended along the trench: flying
trenchwork (formerly known as flying sap) being distinguished from
common trenchwork by the use of gabions, by the help of which
protection could be more quickly obtained. Both these kinds of
trenchwork were commenced at night, the position of the trench having
been previously marked out by tape. The "tasks" or quantities of earth
to be excavated by each man were so calculated that by daybreak the
trench would afford a fair amount of cover. Flying trenchwork was
generally used for the 2nd parallel and its approaches, and as far
beyond it as possible. In proportion as the attack drew nearer to the
covered way, the fire of the defenders' small-arms and wall-pieces
naturally grew more effective, though by this time most of their
artillery would have been dismounted by the fire of the siege
batteries. It therefore became necessary before reaching the 3rd
parallel to have recourse to sap.
[Illustration: FIG. 65.--Regular Attack (Vauban).]
Sapping.
Sapping required trained men. It consisted in gradually pushing
forward the end of a narrow trench in the desired direction. At the
sap-head was a squad of sappers. The leading man excavated a trench 1
ft. 6 in. wide and deep. To protect the head of the trench he had a
shield on wheels, under cover of which he placed the gabions in
position one after another as the sap-head progressed. Other men
following strengthened the parapet with fascines, and increased the
trench to a depth of 3 ft., and a width of 2 ft. 6 in. to 3 ft. Fig.
66, taken from Vauban's treatise on the attack, shows the process
clearly. The sap after being completed to this extent could be widened
at leisure to ordinary trench dimensions by infantry working parties.
[Illustration: FIG. 66.--Sapping (Vauban).]
As the work at the sap-head was very dangerous, Vauban encouraged his
sappers by paying them on the spot at piecework rates, which increased
rapidly in proportion to the risk. He thus stimulated all concerned to
do their best, and reckoned that under average conditions he could
depend on a rate of progress for an ordinary sap of about 50 yds. in
24 hours.
It is interesting to compare the more recent method of sapping with
that above described (fig. 67 taken from the _Instruction in Military
Engineering_, 1896). It is no longer possible to place gabions in
position at the sap-head under fire. Accordingly the leading sapper
excavates to the full depth of 4 ft. 6 in., and the rate of progress
is retarded proportionately, so that an advance of only 15 to 30 yds.
in 24 hours can be reckoned on instead of 50. The head of the sap is
protected by a number of half-filled sandbags, which the leading
sapper throws forward as he goes on.
The nearer the approaches drew to the covered way, the more oblique
became the zig-zags, so that little forward progress was made in
proportion to the length of the trench. The approaches were then
carried straight to the front, by means of the "double sap," which
consisted of two single saps worked together with a parapet on each
side (fig. 68). To protect these from being enfiladed from the front,
traverses had to be left at intervals, usually by turning the two saps
at right angles to right or left for a few feet, then forward, and so
on as shown in fig. 69, the distance apart of these traverses being of
course regulated by the height from which the enemy's fire commanded
the trench.
Later stages of the attack.
The later stages in the attack are illustrated in fig. 70. From the
third parallel the attack was pushed forward up the glacis by means of
the double sap. It was then pushed right and left along the glacis, a
little distance from the crest of the covered way. This was called
"crowning" the covered way, and on the position thus gained breaching
batteries were established in full view of the escarp. While the escarp
was being breached, if it was intended to use a systematic attack
throughout, a mine gallery (see _Mining_ below) was driven under the
covered way and an opening made through the counterscarp into the ditch.
The sap was then pushed across the ditch, and if necessary up the
breach, the defenders' resistance being kept under by musketry and
artillery fire from the covered way. The ravelin and bastions were thus
captured successively, and where the bastions had been retrenched the
same methods were used against the retrenchment.
[Illustration: From _Military Engineering_, by permission of the
Controller of H.M. Stationery Office.