Chapter X: Part 10

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._"

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

II. MODERN PERMANENT FORTIFICATION

High-angle fire with long shell.

Modern fortification dates by universal consent from 1885. The Germans had begun experiments a year or two before this, with long shell containing large charges of gun-cotton. But it was the experiments at Fort Malmaison in France in 1886 that set the military world speculating on the future of fortification. The fort was used as a target for 8-in. shell of five calibres length containing large charges of melinite. The reported effects of these made a tremendous sensation, and it was thought at first that the days of permanent fortification were over. Magazine casemates were destroyed by a single shell, and revetment walls were overturned and practicable breaches made by two or three shells falling behind them. It must be remembered, however, that the works were not adapted to meet this kind of fire. The casemates had enough earth over them to tamp the shell thoroughly, but not enough to prevent it from coming into contact with the masonry, and the latter was not thick enough to resist the explosion of the big charges. Other experiments were made in the same direction in Germany, Holland, Belgium and Austria. The Germans used shell containing from 60 to 130 lb. of high explosive.

After the first alarm had subsided foreign engineers set about adapting their works to meet the new projectiles. Revetments were enormously strengthened, and designed so that their weight resisted overturning. Concrete roofs were made from 6 to 10 ft. thick, and in many cases the surface of the concrete was left bare so as to expose a hard surface to the shell without any earth tamping. The idea of cupolas and shielded guns gained ground, and is now practically accepted all over the continent of Europe. In many cases the main armament, in some only the safety armament (see below), is in cupolas in the forts.

FIG. 44.--Metz in 1899.]

But meanwhile Europe had been flooded with literature on the subject, and the whole policy of fortification as well as its minutest details were discussed _ab ovo_. The extremists of both sides revelled in their opportunity. Some declared that, with the use of heavy guns and armour, fortresses could be made stronger than ever. Others held that modern fortresses were far too expensive, that their use led to strategic mistakes, and (arguing from certain well-known examples) that extemporized field defences could offer as good a resistance as permanent works.

European military opinion generally is now more or less agreed on the following lines:--

1. Important places must be defended by fortresses.

2. Their girdle of forts must be far enough out to prevent the
bombardment of the place.

3. An enceinte is desirable, but need not be elaborate.

4. A few guns (called "safety armament") should be in the forts, and
these must be protected by armour.

5. The bulk of the artillery of the defence should be outside the
forts; the direct-fire guns preferably in cupolas, the howitzers in
concealed positions.

6. The forts should be connected by lines of entrenched infantry
positions and obstacles, permanent bomb-proof shelters being provided
for the infantry.

7. There should be ample communications--radial and
peripheral--between the place and the forts, both by road and rail.

8. Special lines of communication--such as mountain passes--should be
closed by barrier forts.

These considerations will now be taken somewhat more in detail, but first it will be useful to deal with the plan of Metz in 1899 (fig. 44).

Metz.

Here the fortifications of successive periods can be readily
recognized. First the old enceinte, unaltered by the Germans and now
_declassee_. Next the detached forts, begun by the French engineers in
1868 and still unfinished in 1870, can be readily recognized by their
bastioned trace. Among them are Fort Manteuffel, formerly St Julien,
and Fort Goeben (fig. 45), formerly Queuleu. These were not altered in
their general lines.

FIG. 45.--Fort Goeben, Metz.]

This early line of detached forts, less than 3000 yds. from the
enceinte, was completed by the Germans with forts of polygonal type
such as Fort Prinz August. The hill of St Quentin (fig. 46), a very
important point, was converted into a fortified position, with two
forts and connecting parapets, and a communication running north to
Fort Alvensleben.

The arrangement of wing batteries in connexion with the forts can be
clearly noted at Fort Manteuffel. These are reinforced by other
batteries either for the defence of the intervals or to dominate
important lines of approach such as the valley of the Moselle (canal
battery at Montigny). To these were added later armoured batteries.

There are also infantry positions, shelters and magazines in connexion
with this line.

Finally some new forts of modern type were commenced in 1899 at about
9000 yds. from the place.

Fortresses.

Leaving out of consideration at present the strategic use of groups of fortresses, the places which, as mentioned above, are intrinsically worth being defended as fortresses are:--

(a) Centres of national, industrial or military resources.

(b) Places which may serve as _points d'appui_ for manoeuvres.

(c) Points of intersection of important railroads.

(d) Bridges over considerable rivers.

(e) Certain lines of communication across a frontier.

Examples of (a) are Paris, Antwerp, Lyons, Verdun. Again for (a) and (b), as is pointed out by Plessix and Legrand, Metz in the hands of the Germans may serve both as a base of supplies and a _point d'appui_ for one flank. Strassburg is a bridge-head giving the Germans a secure retreat across the Rhine if beaten in the plains of Alsace, and an opportunity of resuming the offensive when they have re-formed behind the river.

FIG. 46.--St Quentin position, Metz.]

The ring of detached forts.

The distance of detached forts from the place depends on the range of the siege artillery and the distance at which it can usually be established from the forts, and is variously given by different continental writers at from 4 to 9 km. (4500 to 10,000 yds.). The bombarding range of siege howitzers with heavy shells is considered to be about 8000 yds., and if it is possible for them to be emplaced within say 2000 yds. of the forts, this would give a minimum distance of 6000 yds. from the forts to the body of the place. Some writers extend the minimum distance to 7 km., or nearly 8000 yds. In practice, however, it must happen that the position of the forts is determined to a very large extent by the lie of the ground. Thus some good positions for forts may be found within 4000 or 5000 yds. of the place, and no others suitable on the same front within 15,000 yds. In that case the question of expense might necessitate choosing the nearer positions. Some examples of the actual distances of existing forts have already been given. Others, more recent, are, at Bucharest 7-10 km., Lyons 8-10(1/2), Copenhagen 7-8 and Paris 14-17. _Strategic pivots_ are in a different category from other fortresses. While not necessarily protected from bombardment, they may yet have one or two forts thrown out from 9 to 12 km., to get advantage of ground. Such are Langres, Epinal and Belfort.

_The Enceinte._--The desirability of this is almost universally
allowed; but often it is more as a concession to tradition than for
any solid reason. The idea is that behind the line of forts, which is
the main defensive position, any favourable points that exist should
be provisionally fortified to assist in a "step-by-step" defence: and
behind these again the body of the place should be surrounded by a
last line of defence, so that the garrison may resist to the last
moment. It may be remarked that apart from the additional expense of
an enceinte, such a position would not, under modern conditions, be
the most favourable for the last stages of a defence. Again, there is
the difficulty that it is practically impossible to shut in a large
modern town by a continuous enceinte. It has been proposed to
construct the enceinte in sections in front of the salient portions of
the place. This system of course abandons several of the chief
advantages claimed for an enceinte.

In actual practice enceintes have been constructed since 1870 in
France and other countries, consisting of a simple wall 10 or 12 ft.
high with a banquette and loopholes at intervals. This of course can
only be looked upon as a measure of police. For war purposes, in face
of modern artillery, it is a _reductio ad absurdum_.

_The Safety Armament._--If the bulk of the artillery is to be placed
in positions prepared on the outbreak of war, it is considered very
necessary that a few heavy long-range guns should be permanently in
position ready at any moment to keep an enemy at a distance, forcing
him to open his first batteries at long range and checking the advance
of his investment line. Such guns would naturally be in secure
positions inside the forts, and if they are to be worked from such
positions they must have armour to shield them from the concentrated
fire of the numerous field artillery that a besieger could bring to
bear from the first.

The question of artillery positions.

Artillery outside the forts constitutes the most important part of the defence, and there is room for much discussion as to whether it should have positions prepared for it beforehand or should be placed in positions selected as the attack develops itself. On the one hand the preparation of the positions beforehand, which in many cases means the use of armour and concrete, increases very largely the initial expense of the defence, and ties the defender somewhat in the special dispositions that become desirable once the attack has taken shape. Moreover, such expenditure must be incurred on all the fronts of the fortress, whereas the results would only be realized on the front or fronts actually attacked. On the other hand much time and labour are involved in emplacing heavy and medium artillery with extemporized protection, and this becomes a serious consideration when one remembers how much work of all kinds is necessary in preparing a fortress against attack. Again, to avoid the danger of a successful attack on the intervals between the forts before their defences have been fully completed, the fire of the guns in the intermediate positions might be urgently required. The solution in any given case would no doubt depend on the importance of the place. In most cases a certain amount of compromise will come in, some preparation being made for batteries, without their being completed. Armoured batteries of whatever kind must in any case be prepared in peace time. It should not be overlooked that as, whatever theories may exist about successive lines of defence, the onus of the defence will now lie on the fort line, just as it formerly did on the enceintes, so that line should be fully prepared, and should not have to commence its fight in a position of inequality.

FIG. 47.]

_Defence of Intervals of Forts._--The frontal fire of the batteries in
the intervals and the flanking fire of some of the guns in the forts
will play an important part, but the main reliance should be on
infantry defence. A fully prepared fortress would have practically a
complete chain of infantry fighting positions and obstacles between
the forts, at all events on the fronts likely to be seriously
attacked. The positions would consist largely of fire trenches, with
good communications; but it is pretty generally recognized that there
must be some _points d'appui_ in the shape of redoubts or infantry
forts, and also bomb-proof shelter for men, ammunition and stores near
the fighting line. This is usually included in the redoubts. If they
are to resist the heaviest shell, such shelters must be built in peace
time.

_Communications_ are of the first importance, not merely to facilitate
the movement of the enormous stores of ammunition and materials
required in the fighting line, but also that defenders may fully
utilize the advantage of acting on interior lines. They should include
both railways and roads running from the centre of the place to the
different sectors of defence, and all round, in rear of the line of
forts; also ample covered approaches to the fighting line. Concealment
is essential, and where the lie of the ground does not help, it must
be got from earth parapets or plantations.

Barrier forts.

The principal use of barrier forts is in country where the necessary line of communication cannot be easily diverted. For instance, in a comparatively flat country a barrier fort commanding a road or railway is of little use because roads may be found passing round it, or a line of railway may be diverted for some miles to avoid it. But in mountainous country, where such diversion is impossible, it will be necessary for the enemy to capture the fort before he can advance; and the impossibility of surrounding it, the few positions from which siege artillery can be brought into play, and the fact that there is practically only one road of approach to be denied, make these positions peculiarly suitable for forts with armoured batteries. Italy makes considerable use of such forts for the defence of frontier passes.

_General Brialmont's Theoretical Claim for the Defence of a
Country._--Before going into details, it is worth while to state the
full claim of strategic fortification advanced by General Brialmont,
the most thorough of all its advocates. It is as follows:--

A. Fortify the capital.

B. Fortify the points where main lines of communication pass a
strategic barrier.

C. Make an entrenched camp at the most important centre of
communication in each zone of invasion: and support it by one or two
places arranged so as to make a fortified district.

FIG. 48.]

D. Close with barrier forts the lines necessary to an enemy across
mountains or marshes.

E. Make a central place behind a mountain chain as a pivot for the
army watching it.

F. Defend mountain roads by provisional fortifications.

G. Make a large place in each theatre of war which is far from the
principal theatre, and where the enemy might wish to establish
himself.

H. Fortify coasts and harbours.

Objections to these proposals will be readily supplied by the
officials of the national treasury and the commanders-in-chief of the
active armies.

Types of detached forts.

So many types of detached forts have been proposed by competent authorities, as well as actually constructed in recent years, that it is impossible here to consider all of them, and a few only will be reproduced of those which are most representative of modern continental thought.

Taking first the type of heavily armed fort, which contains guns for
the artillery fight as well as safety armament, we must give
precedence to General Brialmont. The two works here shown are taken
from the _Progres de la defense des etats, &c._, published in 1898.
The pentagonal fort (fig. 47) has two special features. In section 1
is shown a concrete infantry parapet, with a gallery in which the
defenders of the parapet may take shelter from the bombardment
preceding an assault. In section 2 it will be seen that the
counterscarp galleries flanking the ditch are drawn back from the face
of the counterscarp. This is to counteract proposals that have been
made to obscure the view from the flanking galleries, and perhaps
drive the defenders out of them by throwing smoke-producing materials
into the ditch at the moment of an assault. The arrangement may save
the occupants of the galleries from excessive heat and noxious fumes,
but will not of course prevent the smoke from obscuring the view.

The following points may be noticed about this design in comparing it
with earlier types. There is no escarp, the natural slope of the
rampart being carried down to the bottom of the ditch. There is a
counterscarp to the faces, but no covered way. The flanks have no
counterscarp, but a steel fence at the foot of the slope, and the
covered way which is utilized for a wire entanglement which is under
the fire of the parapet. The gorge has a very slight bastioned
indentation, which allows for an efficient flanking of the ditch by a
couple of machine guns placed in a single casemate on either side.

The abolition of the covered way as such is noteworthy. It marks an
essential difference between the fort and the old enceinte profiles;
showing that offensive action is not expected from the garrison of the
fort, and is the duty of the troops of the intermediate lines.

The great central mass of concrete containing all the casemates and
the gun-cupolas, a very popular feature, is omitted in this design,
advantage being taken of the great lateral extent of the fort to
spread the casemates under the faces, flanks and gorge, with a
communication across the centre of the fort. This arrangement gives
more freedom to the disposition of the cupolas. The thickness of the
concrete over the casemate arches is more than 8 ft. Communication
between the faces and the counterscarp galleries is obtained by
posterns under the ditch. The armament, which is all protected by
cupolas, is powerful. It consists of two 150-mm. (6 in.) guns, four
120-mm. (4.7 in.) guns, two 210-mm. (8.4 in.) howitzers, two 210-mm.
(8.4 in.) mortars, four 57-mm. Q.F. guns for close defence. There is
also a shielded electric light projector in the centre.

This fort is a great advance on General Brialmont's designs before
1885. These were marked by great complexity of earth parapets and
various _chicanes_ which would not long survive bombardment. This type
is simple and powerful. It is also very expensive.

The second Brialmont fort (fig. 48) is selected because it shows a
keep or citadel, an inner work designed to hold out after the capture
of the outer parapet. General Brialmont held strongly to the necessity
of keeps for all important works. History of course gives instances of
citadels which have enabled the garrison to recapture the main work
with assistance, or caused a really useful delay in the progress of
the general attack. It affords still more instances in which the keeps
have made no resistance, or none of any value. Some think that the
existence of a keep encourages the defenders of the main work; others
that it encourages the idea of retreat. The British school of thought
is against keeps. In any case they add largely to expense.

In the present design the keep is a mass of concrete, which depends
for the defence of its front ditches on counterscarp galleries in the
main work, the few embrasures for frontal defence being practically
useless. Its main function is to prevent the attackers from
establishing themselves on the gorge, thus leaving the way open for a
reinforcement from outside to enter (assisted by bamboo flying
bridges) through the passages left for the purpose in the outer and
inner gorge parapets.

As regards the main work, the arrangements for defence of the ditch
and the armament are similar to the design last considered. This
parapet has no concrete shelter for the defenders. The casemates are
all collected in the keep and the gorge, with a passage all round
giving access to the parapet and the cupolas.

FIG. 49.--Fort Molsheim, Strassburg.]

Fig. 49 is a German work, Fort Molsheim at Strassburg. This is a
simple type of triangular fort. The main mass of concrete rests on the
gorge, and is divided by a narrow courtyard to give light and air to
the front casemates. The fort has a medium armament for the artillery
fight, consisting of four 6-in. howitzers in cupolas. On each face are
two small Q.F. guns in cupolas for close defence, for which purpose,
it will be seen, there is also an infantry parapet. At the angles are
look-out turrets. The ditch has escarp and counterscarp, and is
defended by counterscarp galleries at the angles. There is no covered
way. The thickness of concrete over the casemates, where it is
uncovered, is about 10 ft.