Y. A _retrenchment_ with a ditch, of the breach Z.
&. _Traverses_ to protect the terreplein of the ramparts from
enfilade.
Turning back now to the middle of the 16th century we find in the early
examples of the use of the bastion that there is no attempt made to
defend its faces by flanking fire, the curtains being considered the
only weak points of the enceinte. Accordingly, the flanks are arranged
at right angles to the curtain, and the prolongation of the faces
sometimes falls near the middle of it. When it was found that the faces
needed protection, the first attempts to give it were made by erecting
_cavaliers_, or raised parapets, behind the parapet of the curtain or in
the bastions.
[Illustration: FIG. 21.]
The first example of the complete bastioned system is found in
Paciotto's citadel of Antwerp, built in 1568 (fig. 21). Here we have
faces, flanks and curtain in due proportion; the faces long enough to
contain a powerful battery, and the flanks able to defend both curtain
and faces. The weak points of this trace, due to its being arranged on a
small pentagon, are that the terreplein or interior space of the
bastions is rather cramped, and the salient angles too acute.
The 16th century.
In the systems published by Speckle of Strassburg in 1589 we find a
distinct advance. Speckle's actual constructions in fortification are of
no great importance; but he was a great traveller and observer, and in
his work, published just before his death, he has evidently assimilated,
and to some extent improved, the best ideas that had been put forward up
to that time.
Two specimens from Speckle's work are well worth studying as connecting
links between the 16th and 17th centuries.
Fig. 22 is early 16th-century work much improved. There are no
outworks, except the covered way, now fully developed, with a battery
in the re-entering place of arms. The bastions are large, but the
faces directed on the curtain get little protection from the flanks.
To make up for this they are flanked by the large cavaliers in the
middle of the curtain. The careful arrangement of the flank should be
noted; part of it is retired, with two tiers of fire, some of which is
arranged to bear on the face of the bastion. The great saliency of the
bastion is a weak point, but the whole arrangement is simple and
strong.
In the second example, known as Speckle's "reinforced trace" (fig.
23), we find him anticipating the work of the next century. The
ravelin is here introduced, and made so large that its faces are in
prolongation of those of the bastions. Speckle's other favourite
ideas are here: the cavaliers and double parapets and his own
particular invention of the low batteries behind the re-entering place
of arms and the gorge of the ravelin. These low batteries did not find
favour with other writers, being liable to be too easily destroyed by
the besiegers' batteries crowning the salients of the covered way.
Speckle's book is of great importance as embodying the best work of
the period. His own ideas are large and simple, but rather in advance
of the powers of the artillery of his day.
[Illustration: FIG 22.]
The 17th century.
At the beginning of the 17th century we find the Italian engineers
following Paciotto in developing the complete bastioned trace; but they
got on to a bad line of thought in trying to reduce everything to
symmetry and system. The era of geometrical fortification (or, as Sir
George Clarke has called it, "drawing-board" fortification) had already
begun with Marchi, and his followers busied themselves entirely in
finding geometrical solutions for the application of symmetrical
bastioned fronts to such imaginary forms of perimeter as the oval, club,
heart, figure of eight, &c. Marchi, however, was one of the first to
think of prolonging the resistance of a place by means of outworks such
as the ravelin. De Villenoisy says that Busca was the first to discuss
the proportions and functions of all the component parts of a front; and
Floriani, about 1630, was the last of the important Italians. The
characteristics of a good deal of Spanish fortification carried out at
this time were, according to the same authority, that the works were
well adapted to sites, and the masonry excellent but too much exposed,
while the bastions were too small. The Dutch and German schools will be
referred to later.
[Illustration: FIG. 23.--Speckle's Reinforced Trace.]
The French engineers now began to take the lead in adapting the
principles already established to actual sites. In the first half of the
century the names of de Ville and Pagan stand out as having contributed
valuable studies to the advancement of the science. In putting forward
their designs they discussed very fully such practical questions as the
length of the line of defence, whether this should be governed by the
range of artillery or musketry fire, the length of flanks, the use in
them of orillons, casemates and retired flanks, the size of bastions,
&c.
It is the latter half of the 17th century, however, which is one of the
most important periods in the history of fortification, chiefly because
it was illuminated by the work of Vauban. It was at this time also that
a prodigious output of purely theoretical fortification began, which
went on till the French Revolution. Many of the "systems" published at
this time were elaborated by men who had no practical knowledge of the
subject, some of them priests who were engaged in educating the sons of
the upper classes, and who had to teach the elements of fortification
among other things. They naturally wrote treatises, which were valuable
for their clearness of style; and with their industry and ingenuity the
elaboration of existing methods was a very congenial task. Most of these
essays took the form of multiplication and elaboration of outworks on an
impossible scale, and they culminated in such fantastic extravagances as
the system of Rhana, published in 1769 (fig. 24). These proposals,
however, were of no practical importance.
Vauban.
The work of the real masters who knew more than they published can
always be recognized by its comparative simplicity. The greatest of
these was Sebastien le Prestre de Vauban (q.v.). Born in 1633, and
busied from his eighteenth year till his death in 1707 in war or
preparations for war, he earned alike by his genius, his experience, his
industry and his personal character the chief place among modern
military engineers. His experience alone puts him in a category apart
from others. Of this it is enough to say that he took part in
forty-eight sieges, forty of which he directed as chief engineer without
a single failure, and repaired or constructed more than 160 places.
Vauban's genius was essentially practical, and he was no believer in
systems. He would say, "One does not fortify by systems but by common
sense." Of new ideas in fortification he introduced practically none,
but he improved and modified existing ideas with consummate skill in
actual construction. His most original work was in the attack (see
below), which he reduced to a scientific method most certain in its
results. It is therefore one of the ironies of fate that Vauban should
be chiefly known to us by three so-called "systems," known as his
"first," "second" and "third." How far he was from following a system is
shown by de Villenoisy, who reproduces twenty-eight fronts constructed
by him between 1667 and 1698, no two of which are quite alike and most
of which vary very considerably to suit local conditions.
[Illustration: FIG. 24.]
Vauban's "first system," as variously described by other writers even in
his own time, is pieced together from some of the early examples of his
work. The "second system" is the "tower bastion" defence of Belfort and
Landau (1684-1688), obviously suggested by a design of Castriotto's one
hundred years earlier; and the "third system" is the front of
Neu-Breisach (1698), which is merely Landau slightly improved. In other
works, between 1688 and 1698, he did not keep to the tower bastion idea.
It will be convenient to take the "first system," as reproduced in the
Royal Military Academy text book of fortification (fig. 25) as typical
of much of Vauban's work. It may be observed that he sometimes uses the
straight flank, and sometimes the curved flank with orillon. Parapets in
several tiers are never used, nor cavaliers. The ravelin is almost
always used. It is small, having little artillery power and giving no
protection to the shoulders of the bastions. Sometimes it has flanks and
occasionally a keep.
The tenaille is very generally found. In this form, viz. as a shield to
the escarp of the curtain, it was probably invented by him. Fig. 25
shows two forms. In both the parapet of the tenaille had to be kept low,
so that the flanks might defend a breach at the shoulder of the opposite
bastion, with artillery fire striking within 12 ft. of the base of the
escarp. Traverses are used for the first time on the covered way to
guard against enfilade fire; and the re-entering place of arms, to which
Vauban attached considerable importance, is large.
[Illustration: FIG. 25.--Vauban's First System.]
For the construction of the trace an average length of about 400 yds.
(which, however, is a matter entirely dependent on the site) may be
taken for the exterior side. The perpendicular, except for polygons of
less than six sides, is one-sixth, and the faces of the bastions
two-sevenths of the exterior side. The flanks are chords of arcs
struck from the opposite shoulder as centres. An arc described with
the same radius, but with the angle of the flank as a centre, and
cutting the perpendicular produced outwardly, gives the salient of the
ravelin; the prolongations of the faces of the ravelin fall upon the
faces of the bastions at 11 yds. from the shoulders. The main ditch
has a width of 38 yds. at the salient of the bastions, and the
counterscarp is directed upon the shoulders of the adjoining bastions.
The ditch of the ravelin is 24 yds. wide throughout.
As regards the profile the bastions and curtain have a command of 25
ft. over the country, 17 ft. over the crest of the glacis and 8 ft.
over the ravelin. The ditches are 18 ft. deep throughout. The parapets
are 18 ft. thick with full revetments. In his later works he used
demi-revetments.
Fig. 26 shows the tower bastions of Neu-Breisach, or the so-called
"third system." It is worth introducing, simply as showing that even a
mind like Vauban's could not resist in old age the tendency to duplicate
defences. Here the main bastions and tenaille are detached from the
enceinte. The line of the enceinte is broken with flanks and further
flanked by the towers. The ravelin is large and has a keep. The section
through the face of the bastion shows a demi-revetment with wide berm,
and a hedge as an additional obstacle.
18th and 19th centuries.
After Vauban died, though the theories continued, the valuable additions
to the system were few. Among his successors in the early part of the
18th century Cormontaingne (q.v.) has the greatest reputation, though
his experience and authority fell far short of Vauban's. He was a clear
thinker and writer, and the elements of the system were distinctly
advanced by him. His trace includes an enlarged ravelin with flanks, the
ends of which were intended to close the gaps at the end of the
tenaille, and a keep to the ravelin with flanks. He provides a very
large re-entering place of arms, also with a keep, the ditches of which
are carefully traced so as to be protected from enfilade by the salients
of the ravelin and bastion. He was also in favour of a permanent
retrenchment of the gorge of the bastion. His works were printed, with
many alterations, more than twenty years after his death, to serve as a
text-book for the school of Mezieres. This school was established in
1748, and from this time forward there was an official school of
thought, based on Vauban. Cormontaingne's work, therefore, represents
the modifications of Vauban's ideas accepted by French engineers in the
latter part of the 18th century. The school of Mezieres was afterwards
replaced by that of Metz, which carried on its traditions. Such schools
are necessarily conservative, and hence, in spite of the gradual
improvement in ordnance and firearms, we find the main elements of the
bastioned system remaining unchanged right up to the period of the
Franco-German War in 1870. Chasseloup-Laubat tells us that, before the
Revolution, to attempt novelties in fortification was to write one's
self down ignorant. How far the general form of the bastion with its
outworks had become crystallized is evident from a cursory comparison of
fig. 27 with Vauban's early work. This figure is the front of the Metz
school in 1822, by General Noizet.
[Illustration: FIG. 26.--Neu-Breisach.]
[Illustration: FIG. 27.--Noizet.]
Since, therefore, the official view was that the general outlines of the
system were sacred, the efforts of orthodox engineers from
Cormontaingne's time onwards were given to improvements of detail, and
mainly to retard breaching operations as long as possible. We find
enormous pains being bestowed on the study of the comparative heights of
the masonry walls and crest levels; with the introduction here and there
of glacis slopes in the ditches, put in both to facilitate their
defence and to protect portions of the escarps.
Among the unorthodox two names deserve mention. The first of these is
Chasseloup-Laubat (q.v.), who served throughout the wars of the Republic
and Empire, and constructed the fortress of Alessandria in Piedmont.
Chasseloup's main proposals to improve the bastioned system were two:
First, in order to prevent the bastions from being breached through
the gaps made by the ditch of the ravelin, he threw forward the
ravelin and its keep outside the main glacis. This had the further
advantage of giving great saliency to the ravelin for cross-fire over
the terrain of the attack. On the other hand, it made the ravelin
liable to capture by the gorge. It is probable that this system would
have lent itself to a splendid defence by an able commander with a
strong force; but under the opposite conditions it has a dangerous
element of weakness.
Secondly, in order to get freedom to use longer fronts than those
admissible for the ordinary bastioned trace, he proposed to extend his
exterior side up to about 650 yds. and to break the faces of his
bastions; the portion next the shoulder being defended from the flank
of the collateral bastion and coinciding with the line of defence, and
the portion next the salient, up to about 80 yds. in length, being
defended from a central keep or caponier placed in front of the
tenaille. The natural criticism of this arrangement is that it
combines some of the defects of both the bastioned and polygonal
systems without getting the full advantages of either.
[Illustration: FIG. 28.--Chasseloup-Laubat.
Fig. 28 shows a half front of Chasseloup's system, of ordinary length,
as actually constructed. The section shows an interesting detail, viz.
the Chasseloup mask--a detached mask with tunnels for the casemate
guns to fire through, the intention of which is to save them from
being destroyed from a distance.
The second name is that of Captain Choumara of the French Engineers,
born in 1787, whose work was published in 1827. Two leading ideas are
due to him. The first is that of the "independence of parapets." A
glance at any of the plans that have already been shown will show that
hitherto the crests of parapets had always been traced parallel to the
escarp or magistral line. Choumara pointed out that, while it was
necessary for the escarp to be traced in straight lines with reference
to the flanking arrangements, there was no such necessity as regards the
parapets. By making the crest of the parapet quite independent of the
escarp line he obtained great freedom of direction for his fire. The
second idea is that of the "inner glacis." This was a glacis parapet
placed in the main ditch to shield the escarp; its effect being to
prevent the escarp of the body of the place from being breached in the
usual way by batteries crowning the crest of the covered way.
The need for Choumara's improvements has passed by, but he was in his
time a real teacher. One sentence of his strikes a resounding note:
"What is chiefly required in fortification is simplicity and strength.
It is not on a few little contrivances carefully hidden that one can
rely for a good defence. _The fate of a place should not depend on the
intelligence of a corporal shut up in a small post prepared for his
detachment._"
[Illustration: FIG. 29.--Sedan in 1705.]
Before leaving the bastioned system it will be of interest to study a
couple of actual and complete examples, one irregular and one regular.
Fig. 29 shows the defences of Sedan as they were at the end of the
17th century. One sees the touch of Vauban here and there, but the
work is for the most part apparently early 17th century. It will be
observed that on the river side of the town the defence consists of
very irregular bastions with duplicated wet ditches (see the Dutch
style, below); and on the other side, where water is not available,
strength is sought for by pushing a succession of hornworks far out.
Fig. 30 is Saarlouis, constructed by Vauban in 1680 in his early
manner, a remarkable example of symmetry. Vauban of course never
thought of aiming at symmetry, which is of itself neither good nor
bad, but it is interesting to note such a perfect example of the
system.
It must here be remarked that the reproach of "geometrical"
fortification is in no way applicable to the works of Vauban and his
immediate successors. The true geometric fortification, which
worshipped symmetry as a fetish, marked, as has been already pointed
out, the decadence of the Italian school. Vauban and his fellows
excelled in adapting works to sites, the real test of the engineer.
The bastioned system was the 17th-century solution of the
fortification problem. Given an artillery and musketry of short range
and too slow for effective frontal defence, a ditch is necessary as an
obstacle. What is the best means of flanking the ditch and of
protecting the flanking arrangements? If Vauban elected for the
bastion, we must before criticizing his choice remember that he was
the most experienced engineer of his day, a man of the first ability
and quite without prejudice. What is matter for regret is that the
authority of Vauban should have practically paralysed the French
school during the 18th and most of the 19th century, so that while the
conditions of attack and defence were gradually altering they could
admit no change of idea, and their best men, who could not help being
original, were struggling against the whole weight of official
opposition.
Again, such duplication of outworks as we see at Sedan is not
geometric fortification. It is a definite attempt to retard the
attack, on ground favourable to it, by successive lines of defence. As
to the policy of this, no axiom can be laid down. Nowadays most of us
think, as Machiavelli did, that a single line of defence is best and
that a second line only serves to suggest the advisability of
retreat. There are also, of course, the recognized drawbacks of
outworks, difficulty of retreat, of relief and so forth, and the moral
effect of their loss. But the engineers of such defences as Ostend and
Candia might well say, "Oh, if only when we had held on to that
bastion for so many months we had had a second and a third line of
permanent retrenchment to fall back upon, we could have held the place
for ever." And who shall say that they were wrong? Let us at all
events remember that the leading engineers of that time were men who
had passed their lives in a state of war, and that we ourselves in
comparison with them are the theorists.
[Illustration: FIG. 30.]
The Dutch school.
From the end of the 16th century the Dutch methods of fortification
acquired a great reputation, thanks to the stout resistance offered to
the Spaniards by some of their fortresses, the three years' defence of
Ostend being perhaps the most striking example. Prolonged defences,
which were mainly due to the desperate energy of the besieged, were
credited to the quality of their defences. In point of fact the Dutch
owed more to nature, and more still to their own spirit, than to art;
but they showed a good deal of skill in adapting recent ideas to their
needs.
Three conditions governed the development of the Dutch works at this
time, viz. want of time, want of money and abundance of water. When the
Netherlands began their revolt against Spain, they would no doubt have
been glad enough of expensive masonry fortresses on such models as
Paciotto's citadel of Antwerp. But there was neither time nor money for
such works. Something had to be extemporized, and fortunately for them
they had wet ditches to take the place of high revetted walls.
Everywhere water was near the surface, and rivers or canals were
available for inundations. A wide and shallow ditch, while making a good
obstacle, was also the readiest means of obtaining earth for the
ramparts. High command was, owing to the flatness of the country,
unnecessary and even undesirable, as it did not allow of grazing fire.
What the Dutch actually did in strengthening their towns gives little
evidence of system. Starting as a rule from an existing enceinte,
sometimes a medieval wall, they would provide a broad wet ditch. No
further provision was usually made on the sides of the town which were
additionally protected by a river or inundation. On the other sides the
wet ditch was made still broader, and sometimes contained a
counterguard, sometimes ravelins and lunettes. These were quite
irregular in their design and relation to each other. At the foot of the
glacis would be found another but narrower wet ditch, which was a
peculiarly Dutch feature; and sometimes if the town was in a bend of a
river there would be a canal cut across the bend in a straight line,
strengthened by several redans.
Speaking generally, they endeavoured to provide for the want of a
first-class masonry obstacle by multiplication of wet ditches, and
further to strengthen these obstacles by great quantities of palisading,
for which purpose the timber of old ships was used. They also recognized
the inherent weaknesses of wet ditches, as, for instance, that when
frozen they no longer provide an obstacle; and they studied the means,
not only of causing inundations, but also of arranging to empty as well
as to fill the ditches at will. Simon Stevin was the leader in this
work.
Nevertheless a Dutch school of design did come into existence at this
time. The leaders, early in the 17th century, were Simon Stevin, Maurice
and Henry of Nassau, Marollois and Freitag. The fortress of Coevorden,
constructed by Prince Maurice, of which fig. 31 shows a front, is a
well-known example of this, and the section shows clearly some typical
features of the school.
[Illustration: FIG. 31.--Coevorden.]
The elements of the plan are those of the early bastioned trace, but
we find added both ravelins and lunettes, very regular in design.
There is also the ditch at the foot of the glacis, and surrounding the
rampart of the enceinte a continuous fausse-braie. This work, which
partook of the nature of both boulevard and counterguard, served
several purposes. It was desirable that the weight of the rampart
should be drawn back a little from the edge of the ditch, and the
fausse-braie filled what would otherwise have been dead ground at the
foot of the rampart. It also afforded a grazing fire over the ditch,
which was very important, and which the rampart supported by a
plunging fire.
Coehoorn.
Coehoorn (q.v.), the contemporary and nearest rival to Vauban, was the
greatest light of the Dutch school. Like Vauban he was distinguished as
a fighting engineer, both in attack and defence; but in the attack he
differed from him in relying more on powerful artillery fire than
systematic earthworks. He introduced the Coehoorn mortar. His "first
system," which was employed at Mannheim (fig. 32), is reproduced for the
sake of comparison with the Coevorden front designed a hundred years
earlier. Among other points will be noticed the combination of wet and
dry ditches; the very broad main ditch with counterguard; the roomy keep
of the ravelin; the expansion of the fausse-brais into an independent
low parapet; and the powerful flanking fire in three tiers.
[Illustration: FIG. 32.--Coehoorn's First System.]
German school.
The "tenaille" system and the "polygonal" system which grew out of it
are mainly identified with the _German school_. That school, says von
Zastrow, does not, like that of France, represent the authoritative
teaching of an official establishment, but rather the general practice
of the German engineers. It was founded on the principles of Durer,
Speckle and especially Rimpler, and much influenced in execution by
Montalembert. "The German engineers desired a simple trace, a strong
fortification with retrenchments and keeps, bomb-proof accommodation and
an organization suitable for an offensive defence."
These had always been the German principles. Already in the 16th century
the Prussian defences of Kustrin, Spandau and Peitz had large bomb-proof
casemates sufficient for a great part of the garrison. The same thing is
seen in the defences of Giogau, Schweidnitz, &c., built by Frederick the
Great. These works show various applications of the tenaille system. In
1776 Frederick became acquainted with the work of Montalembert, and his
influence is seen in the casemates of Kosel.
Whether through the influence of Albert Durer or not cannot be said, but
while the bastion was being developed in France the tenaille and the
accompanying casemates from the first found acceptance in Germany, and
thence in eastern and northern Europe. De Groote, who wrote in 1618,
produced a sort of tenaille system, and may have been the inspiration of
Rimpler. Dillich (1640), Landsberg the elder (1648), Griendel d'Aach
(1677), Werthmuller (1685) and others advocated both bastion and
tenaille, sometimes in combination; the German bastion being usually
distinguished by short faces and long flanks.
Rimpler, who was present at the siege of Candia (taken by the Turks in
1669) and died at that of Vienna in 1683, exercised a great influence.
He had been struck by the weakness of the early Italian bastions at
Candia, and published a book in 1673 called _Fortification with Central
Bastions_, which was practically the polygonal trace. Zastrow thinks
that Rimpler inspired Montalembert. He left unfortunately no designs to
illustrate his ideas.
[Illustration: FIG. 33.]
Landsberg the younger (1670-1746), a major-general in the Prussian
service, who saw many sieges, also had a great influence. He appears to
have been the first who frankly advocated the tenaille alone, chiefly on
the ground that the flank, which was the most important part of the
bastioned system, was also the weakest. Fig. 33 shows his system,
published in 1712.
Montalembert and Carnot.
It was, however, ultimately a Frenchman, Marc Rene Montalembert (q.v.),
who was the great apostle of the tenaille, though in his later years he
leaned more to the polygonal trace. He objected to the bastioned trace
on many grounds; principally that the bastion was a shell trap, that the
flanks by crossing their fire lost the advantage of the full range of
their weapons, and that the curtain was useless for defence. He took the
view that the bastions with their ravelins constituted practically a
tenaille trace, spoilt by the detachment of the ravelins and cramped by
the presence of the curtains and flanks. His tenaille system consisted
of redans, with salient angles of 60 deg. or more, flanking each other at
right angles; from which he gave to his system the name of
"perpendicular fortification."
Lazare Carnot (q.v.), the "Organizer of Victory," was, in
fortification, a follower of Montalembert, and produced in 1797 a
tenaille system (fig. 34) on strong and simple lines.
[Illustration: FIG. 34.]
In 1812 Carnot offered three systems. For a dry and level site he
recommended a bastioned trace; but for wet ditches and for irregular
ground, tenaille traces. Both of these latter differ from his 1797
trace in that the re-entering angle is reinforced by a tenaille whose
faces are parallel to the main faces and reach almost to the salients.
There are also counterguards in front of the salients, whose ends
overlap the ends of the tenaille. (N.B. To avoid confusion between the
_tenaille trace_ and the _tenaille_, it should be noted that the
latter is a low detached parapet placed in front of the escarp of the
body of the place, partly as a shield, and partly as an additional
line of defence. It is used in front of the curtain in the bastioned
trace, and in the re-entering angle in the tenaille trace.)
Other important features of Carnot's work were: a continuous general
retrenchment, or interior parapet, following more or less the lines of
the main parapet; the use of the detached wall in place of the escarp
revetment; and the countersloping glacis. This last (of which Carnot
was not the inventor), instead of sloping gently outwards from a crest
raised about 8 ft. down to the natural level of the ground, sloped
inwards from the ground-level to the bottom of the ditch. The
advantage of the additional obstacle of the counterscarp was thus lost
to the defence. On the other hand, the besiegers' saps, as they
progressed down the glacis, were exposed to a plunging fire from the
parapet.
[Illustration: FIG. 35.--Mortar-casemate and Detached Wall.]
Carnot was also, like Coehoorn, a great believer in the mortar; but
while Coehoorn introduced the small portable mortar that bears his name,
Carnot expected great results from a 13 in. mortar throwing 600 iron
balls at each discharge. He endeavoured to prove mathematically that the
discharge of these mortars would in due course kill off the whole of the
besieging force. These mortars he emplaced in open fronted
mortar-casemates, in concealed positions. Fig. 35 shows in section one
of these mortar-casemates, placed between the parapet of the
retrenchment and a detached wall.
[Illustration: FIG. 36.--Montalembert, 1786.]
The polygonal trace.
The leading idea of Montalembert was that for a successful defence it
was necessary for the artillery to be superior to that of the enemy.
This idea led him to the adoption of casemates in several tiers; in
preference to open parapets, exposed to artillery fire of all kinds,
high angle, ricochet and reverse. In considering the defects of bastions
he had arrived at the conclusion that for flanking purposes two forms of
trace were preferable; either the tenaille form, connecting the ravelins
with the body of the place, or the form in which the primary flanking
elements, instead of facing each other with overlapping fire, as with
the bastions, should be placed back to back in the middle of the
exterior side. Fig. 36 is an example of this. The central flanking work
resulting from this arrangement is the caponier of the early Italians,
reintroduced and developed; and with it Montalembert laid the foundation
of the polygonal system of our own time.
Montalembert was one of the first to foresee the coming necessity for
detached forts, and it was for these that he chiefly proposed to use
his caponier flanking, preferring the tenaille system for large places.
In abandoning the bastioned trace he was already committed to the
principle of casemate defence for ditches; and the combination of this
principle with his desire for an overwhelming artillery defence led him
in the course of years of controversial writing into somewhat
extravagant proposals. For instance, for a square fort of about 400 yds.
side, he proposed over 1000 casemate guns; and one of his caponier
sections shows 10 tiers of masonry gun-casemates one above the other.
Confiding in the power of such an artillery, he freely exposed the upper
parts of his casemates to direct fire.
Montalembert is said to have contributed more new ideas to fortification
than any other man. His designs must be considered in some ways
unworkable and unsound, but all the best work of the 19th century rests
on his teaching. The Germans, who already used the tenaille system and
made free provision of bomb-proof casemates, took from him the polygonal
trace and the idea of the entrenched camp.
The polygonal system in fortification implies straight or slightly
broken exterior sides, flanked by casemated caponiers. The caponier is
the vital point of the front, and is protected in important works by a
ravelin and keep. The essence of the system is its simplicity, which
allows of its being applied to any sort of ground, level or broken, and
to long or short fronts.
[Illustration: FIG. 37.--Front at Posen.]
1815-1855, entrenched camps.
The final period of smooth bore artillery is an important one in the
history of fortification. It is true that the many expensive works that
were constructed at this time were obsolete almost as soon as they were
finished; but this was inevitable, thanks to the pace at which the world
was travelling. After the Napoleonic wars the Germanic Confederation
began to strengthen its frontiers; and considering that they had not
derived much strategic advantage from their existing fortresses, the
Germans took up Montalembert's idea of entrenched camps, utilizing at
the same time his polygonal system with modifications for the main
enceintes. The Prussians began with the fortresses of Coblenz and
Cologne; later Posen, Konigsberg and other places were treated on the
same lines. The Austrians constructed, among other places, Linz and
Verona. The Germanic Confederation reinforced Mainz with improved works,
and reorganized entirely Rastatt and Ulm. The Bavarians built
Germersheim and Ingolstadt. While all these works were conceived in the
spirit of Rimpler and Montalembert, they showed the differences of
national temperament. The Prussian works, simple in design, relied upon
powerful artillery fire, and exposed a good deal of masonry to the
enemy's view. The Austrians covered part of their masonry with earth and
gave more attention to detail.
The German development of the polygonal system at this time is not of
great importance, since the great masonry caponiers were designed
without sufficient consideration for the increasing powers of artillery.
One example (fig. 37) is given for the sake of historical comparison. It
is a front of Posen.
"The exterior side of the front is about 650 yds. (600 metres) long.
It is flanked by a central caponier, which is protected by a _detached
bastion_.... The main front is broken back to flank the faces of the
bastion from casemates behind the escarp, as well as from the parapet.
Posen.
"The central caponier forms the keep of the whole front and sweeps
both the interior and the ditch by its flanking fire. It has two
floors of gun-casemates and one for musketry, and on the top is a
parapet completely commanding alike the outworks and the body of the
place. It contains barrack accommodation for a battalion of 1000 men,
and has a large inner courtyard closed at the gorge by a detached
wall. The caponier is itself flanked by three small caponiers at the
head, and one at the inner end of each flank.
"The escarp of the body of the place is a simple detached wall; that
of the detached bastion is either a detached wall with piers and
arches, or a counter-arched revetment. At the salient of the bastion
there is a mortar battery under the rampart, and a casemated traverse
for howitzers upon the terreplein. The flanks of the bastion are
parallel to those of the caponier, and at the same distance from it as
the faces.
"Masonry blockhouses, loopholed for musketry, are provided as keeps of
the re-entering and salient places of arms. In the latter case they
have stairs leading down into a counterscarp gallery, which serves as
a base for countermine galleries, and is connected with the detached
bastion by a gallery under the ditch. The counterscarp is not revetted
if the ditch is wet.
"The angle of the polygon should not be less than 160 deg., in order
that the prolongation of the main ditch may fall within the salients
of the detached bastions of the neighbouring fronts, and the masonry
of the caponiers may thus be hidden from outside view." (R.M.A.
_Text-book of F. & M.E._, 1886.)
The detached fort.
We have now reached a period when the "detached fort" becomes of more
importance than the organization of the enceinte. The early conception
of the role of detached forts in connexion with the fortress was to form
an entrenched camp within which an army corps could seek safety if
necessary. The idea had occurred to Vauban, who added to the permanent
defences of Toulon a large camp defended by field parapets attached to
one side of the fortress. The substitution of a ring of detached forts,
while giving it the greater safety of permanent instead of field
defences, gave also a wider area and freer scope for the operations of
an army seeking shelter under the guns of a fortress, and at the same
time made siege more difficult by increasing the line of investment. The
use of the detached fort as a means of protecting the body of the place
from bombardment had not yet been made necessary by increased range of
artillery.
When these detached forts were first used by Germany the scope of the
idea had evidently not been realised, as they were placed much too close
to the fortress. Those at Cologne, for instance, were only some 400 or
500 yds. in advance of the ramparts. The same leading idea is seen in
most of these forts as in the new enceintes; i.e. a lunette, with a
casemated keep at the gorge. The keep is the essential part of the work,
the rampart of the lunette serving to protect it from frontal artillery
fire. The keep projects to the rear, so as not only to be able to flank
its own gorge, but to give some support to the neighbouring works with
guns protected from frontal fire. This is a valuable arrangement, which
is still sometimes used. The front ditches of the lunettes were flanked
by caponiers. Some of the larger forts were simple quadrangular works
with casemate barracks and caponier ditch defence.
In 1830, in Austria, the archduke Maximilian made an entirely fresh
departure with the defences of Linz. The idea was to provide an
entrenched camp at the least possible cost, whose works should require
the smallest possible garrison. With this object Linz was surrounded
with a belt of circular towers spaced about 600 yds. apart. The towers,
25 metres in diameter, were enclosed by a ditch and glacis, and
contained 3 tiers of casemates. The masonry was concealed from view by
the ditch and glacis. On the top of the tower was an earth parapet, over
which a battery of 13 guns fired _en barbette_. In order to find room
for so many guns in the restricted space, the whole 13 were placed
parallel and close together on a single specially designed mounting.
This new departure was received with a certain amount of approval at the
time, which is somewhat difficult to account for, as a more faulty
system could hardly be devised; but the experiment was never repeated.
The credit for much of the clear views and real progress made in Germany
during this period is due to General von Brese-Winiari,
inspector-general of the Prussian engineers.
France, for a few years after 1815, could spare little money for
fortifications, and nothing was done but repairs and minor improvements
on the old lines. Belgium, having some money in hand, rebuilt and
improved in detail a number of bastioned fortresses which had fallen
into disrepair.
[Illustration: FIG. 38. The Fortress of Antwerp.]
In 1830 France began to follow the lead of Germany with entrenched
camps. The enceinte of Paris was reconstructed, and detached forts were
added at a cost, according to von Zastrow, of L8,000,000. The Belgian
and German frontiers of France being considered fairly protected by the
existing fortresses, they turned their attention to the Swiss and
Italian frontiers, and constructed three fortresses with detached forts
at Belfort, Besancon and Grenoble. The cost of the new works at Lyons
was, according to the same writer, L1,000,000 without the armament. Here
and elsewhere the enceinte was simplified on account of the advanced
defences. That of Paris, which was influenced by political
considerations, was a simple bastioned trace with rather long fronts and
without ravelins or other outworks; the escarp was high and therefore
exposed, and the counterscarp was not revetted.
As regards the detached forts there was certainly a want of clearness of
conception. Those of Paris were simply fortresses in miniature, square
or pentagonal figures with bastioned fronts and containing defensible
barracks. Those of Lyons were much more carefully designed, but the
authors wavered between two ideas. Unwilling to give up the bastion, but
evidently hankering after the new caponiers, they produced a type which
it is difficult to praise. The larger works were irregular four- or
five-sided figures with bastioned fronts; and practically the whole
interior space was taken up by a large keep, with its ditch, on the
polygonal system. The smaller works, instead of a keep, had defensible
barracks in the gorge.
[Illustration: FIG. 39.]
Period from 1855 to 1870.
During the period 1855-1870 a considerable impulse was given to the
science of fortification, both by the Crimean War and the arrival of the
rifled gun. One immediate result of these was the condemnation of
masonry exposed to artillery fire. The most important work of the period
was the new scheme of defence of Antwerp, initiated in 1859. This is
chiefly interesting as giving us the last and finest expression of the
medieval enceinte, at a time when the war between the polygonal and
bastioned traces was still raging, though the boom of the long-range
guns had already given warning that a new era had begun. Antwerp is also
associated with the name of General Brialmont (q.v.), of the Belgian
engineers, whom posterity will no doubt regard as the greatest writer on
fortification of the latter half of the 19th century.
Antwerp.
We give in figs. 38, 39 and 40 the general plan of the 1859 defences of
Antwerp, the plan of a front of the enceinte, and its sections, as
showing almost the last word of fortification before the arrival of high
explosives.
The defences of Antwerp were designed, as the strategic centre of the
national defence of Belgium, for an entrenched camp for 100,000 men. The
length of the enceinte is about 9 m. The detached forts, which on the
sides not defended by inundation are about 1-1/4 m. apart and from 2 to
3 m. in front of the enceinte, are powerful works, arranged for a
garrison of 1000 men. They have each a frontal crest-line of over 700
yds. and are intended for an armament of 120 guns and 15 mortars.
[Illustration: FIG. 40.--Sections of fig. 39.]
The general arrangement of the fronts of the enceinte should be
compared with the earlier German type of Posen. It will be noticed
that while the large casemated caponier at Posen breaks the enceinte
and flanks it both without and within, at Antwerp the caponier is
detached--a much sounder arrangement--and flanks the front only. The
defence of the faces rests on the width of the wet ditches and on the
flanking power of the caponier; there is no attempt to add to it by
fausse-braie or detached wall. The dimensions are everywhere very
generous, allowing free movement for the troops of the defence; the
covered way is 22 yds. wide and there is a double terreplein on the
face. The parapet of the face is 27 ft. thick. The masonry of the
casemate guns in the caponier, first flank and low battery, is
protected by earth, _a la_ Haxo.
In 1859 Austria acknowledged the influence of the new artillery with
some new forts at Verona. The detached forts built by Radetzky in 1848
were only from 1000 to 2000 yds. distant from the ramparts. Those now
added, of which fig. 41 is an example, were from 3000 to 4000 yds. out.
[Illustration: FIG. 41.--Austrian Fort at Verona.]
In the same year the land defences of some of the British dockyards were
taken in hand. These first serious attempts at permanent fortification
in England were received with approval on the continent, as constituting
an advance on anything that had been done before. The detached forts
intended to keep an enemy outside bombarding distance were roomy works
with small keeps. The parapets were organized for artillery and the
ditches were defended by caponiers or counterscarp galleries. The forts
were spaced about a mile apart and arranged so as to support each other
by their fire.
Period from 1870 to 1885.
The sieges of the Franco-German War of 1870 are alluded to in the
section below dealing with the "Attack of Fortresses." As regards their
effect on the designs of fortification the most important thing to note
is the distance to which it was thought necessary to throw out the
detached forts. These distances were of course influenced by the
character of the ground, but for the most part they were very largely
increased. Thus at Paris the fort at St Cyr was 18,000 yds. from the
enceinte; at Verdun the distances varied from 2300 to 12,000 yds.; at
Belfort the new forts were from 4500 to 11,500 yds. out; at Metz 2300 to
4500; and at Strassburg 5200 to 10,000. One result of these increased
distances was of course to increase very largely the length of the zone
of investment, and therefore the strength necessary for the besieging
force.
As regards the character of the works, the typical shape adopted both in
France and Germany was a very obtuse-angled lunette, shallow from front
to rear. The German type had one parapet only, which was organized for
artillery and heavily traversed, the living casemates being under this
parapet. The ditch defence was provided for by caponiers and a detached
wall (see fig. 42).
The French forts had two parapets, that in the rear being placed over
living casemates (in two tiers, as shown in the section of fig. 43 by a
dotted line), and commanding the front one. There was a long controversy
as to whether the artillery of the fort should be on the upper or the
lower parapet, the advocates of the upper parapet attaching great
importance to the command that the guns would have over the country in
front. The other school, objecting to having guns on the skyline,
preferred to sacrifice the command and place them on the lower parapet,
as in fig. 43, the infantry occupying the upper parapet. It will be
observed that the bastioned trace is abandoned, the ditches, like those
of the German fort, being defended by caponiers.
[Illustration: FIG. 42.--German Fort about 1880.]
[Illustration: FIG. 43.--French Fort about 1880.]
While a great deal of work was done on these lines, a very active
controversy had already begun on the general question as to whether guns
should be employed in forts at all. Some declared that the accuracy and
power of artillery had already developed so far, that guns in fixed and
visible positions must needs be put out of action in a very short time.
The remedy proposed by these was the removal of the guns from the forts
into "wing-batteries" which should be less conspicuous; but soon the
broader idea was put forward of placing the guns in concealed positions
and moving them from one to another by means of previously prepared
roads or railways. Others declared that there was no safety for the guns
outside the forts, and that the use of steel turrets and disappearing
cupolas was the only solution of the difficulty. General Brialmont, who
had by this time become the first European authority on fortification
questions, ranged himself on the side of the turrets. The younger
school were largely in favour of mobility and expressed themselves
eagerly in a shower of pamphlets.
It was at this juncture that a new factor was introduced, namely, the
obus-torpille, or long shell with high-explosive bursting charge. With
its appearance we say good-bye to the old school and enter upon the
consideration of the fortification of to-day.