Friedrich Engels

Fortification

Written May to about 9 June 1859.

From the English.

[“The New American Cyclopædia”, Volume VII]

Fortification.
— This field is sometimes divided into defensive fortification, which permits a given place to be put, permanently or for a short time, into a defensible state, and offensive fortification, which contains the rules for conducting a siege. We shall, however, treat it under the following three main heads: permanent fortification, or the art of putting a place in peacetime into such a defensible state as to compel the enemy to attack by a formal siege; the art of siegecraft; and field fortification, or the erection of temporary works to strengthen a given point according to the importance it may acquire under the particular circumstances of a campaign.

I. Permanent Fortification

The oldest form of fortification is probably the stockade, which was in general use among the Turks until the end of the 18th century (palanka) and is still employed to this day on the Indo-Chinese peninsula by the Burmese. It consists of a double or triple row of strong trunks of trees, set upright and close together in the earth, forming a rampart around the place or camp to be defended. Such stockades were encountered by Darius in his expedition against the Scythians, by Cortez at Tabasco in Mexico, and by Captain Cook in New Zealand. Sometimes the space between the rows of trunks was filled with earth; in other cases the stems were connected and held together by wickerwork. The next step was the erection of stone walls instead of the palisades. This construction afforded greater solidity and at the same time made an assault far more difficult; from the time of Nineveh and Babylon up to the close of the Middle Ages, stone walls formed the exclusive means of fortification among all the more civilised peoples. The walls were high enough to render scaling difficult. They were thick enough to offer prolonged resistance to the battering-ram and to allow the defenders to move freely along the rampart, where they were protected by a thinner stone parapet, provided with battlements, through whose embrasures arrows and other missiles could be shot or cast at the assailants. For better defence, the parapet was soon afterwards built overhanging, with openings between the projecting stones on which it rested, so that the besieged were enabled to see the foot of the wall and to fire vertically upon an enemy who had advanced that far. The ditch, which encompassed the entire rampart and formed the chief obstacle to penetration from without, was undoubtedly known at an early period as well. Finally, the defensive capacity of the stone walls was enormously increased by building towers at certain intervals and making them project beyond the wall; this permitted flanking fire by missiles which could be hurled from the towers upon troops attacking the space between two towers. In most cases higher than the wall and separated from its rampart walk by traverse parapets, they commanded the wall and each formed a small fortress which had to be taken separately if the defenders had already been driven from the main rampart. When we add that in some towns, particularly in Greece, there was a kind of citadel on a commanding height within the walls (Acropolis), forming a redoubt and a second line of defence, we have indicated the most essential features of the epoch of masonry fortification.

It was not until the period from the 14th to the end of the 16th century that the introduction of artillery fundamentally changed the methods of attacking fortified places. From that time dates the extensive literature on the art of fortification, which has produced innumerable systems and manners; some of them found a more or less extensive application in practice, while others — and not always the most foolish — were passed over merely as theoretical curiosities, until the fruitful ideas they contained were taken up again at a later period by more fortunate successors. Such, as we shall see, was the fate even of the author who, if we may so call it, built the bridge between the old masonry system and the new system of earthworks faced with masonry only at those points which the enemy cannot see from a distance. The first effect of the introduction of artillery was to increase the thickness of the walls and to enlarge the diameter of the towers at the expense of their height. These towers were now called roundels (rondelli) and were built large enough to accommodate several guns. In order to enable the besieged to use artillery on the rampart as well, an earthwork was thrown up behind it to give it the necessary width. We shall soon see how this earthwork gradually took possession of the stone rampart and in some cases completely displaced it.

Albrecht Dürer, the celebrated German painter, developed this system of roundels to its highest perfection. He made the roundels into completely independent forts, interrupting the continuity of the wall at regular intervals and, provided with casemated batteries, sweeping the ditch; his masonry parapets are not higher than 3 feet uncovered (i.e., visible to the besieger and exposed to his direct fire); to complete the defence of the ditch, he proposed caponnières, casemates on the bottom of the ditch, concealed from the eyes of the besiegers, with embrasures on each side, so as to enfilade the ditch as far as the next angle of the polygon.

Almost all these proposals were new inventions; and although none of them except the casemates were taken into consideration in his time, we shall nevertheless see that they have all been incorporated in the newest and most important systems of fortification and developed in accordance with the changed conditions of modern times.

About the same time the ground plan of the enlarged towers was changed, which may be regarded as the beginning of modern systems of fortification. The round form had the disadvantage that neither the curtain (the piece of wall between two towers) nor the two adjacent towers could, with their fire, reach every point in front of the intermediate tower; there were small angles near the wall where the enemy, once he had advanced that far, could no longer be reached by the fire of the fortress. To avoid this, the tower was converted into an irregular pentagon, one side facing the interior of the fortress and four facing the open country. This pentagon was called a bastion. To avoid repetitions and obscurity, we shall at once give the description and designations of bastioned defence by means of one of those systems which exhibit all its essential details. Figure 1 shows three fronts of a hexagon, fortified after Vauban’s first manner. The left side represents the simple outline used in the geometrical sketch of the work; the right gives the rampart arrangements, the glacis, etc., in detail.

The entire side f' f" of the polygon is not formed by a continuous rampart; at each end the portions d' f' and e" f" are left open, and the resulting gap is closed by the projecting pentagonal bastion d' b' a' c' e'. The lines a' b' and a' c' form the faces, the lines b' d' and c' e' the flanks of the bastion. The points where faces and flanks meet are called the shoulder points. The line a' f', which runs from the centre of the circle to the point of the bastion, is called the capital. The line e" d', which forms part of the original perimeter of the hexagon, is the curtain. Thus each polygon will have as many bastions as sides. The bastion may be either full, when the entire pentagon is filled with earth up to the level of the terreplein (rampart walk) of the rampart (the place where the guns stand), or hollow (empty), when the rampart immediately behind the guns falls away towards the interior. Figure 1 d h a c e shows a full bastion; the next one to the right, only half visible, is a hollow bastion. Bastions and curtains together form the enceinte (core enclosure) or body of the fortress. The first thing we notice on the rampart walk is the parapet, erected towards the front to protect the defenders, and then, on the interior slope (s s), the ramps, by which communications with the interior are maintained. The rampart is high enough to protect the houses of the town from direct fire, and the parapet strong enough to offer prolonged resistance to heavy artillery. All round the rampart runs the ditch t t t t, with several different outworks. First comes the ravelin or demi-lune (half-moon) k l m, before the curtain, a triangular work with two faces k l and l m, each provided with a rampart and a parapet for artillery. The open rear side of every work is called the gorge; thus in the ravelin k m, in the bastion d e. The parapet of the ravelin is about 3 or 4 feet lower than the parapet of the body of the fortress, so that the ravelin is commanded by the curtain and the guns of the latter can, if necessary, fire over it. In the ditch between the curtain and the ravelin lies an elongated and narrow detached work, the tenaille (pincer, or shears work) g h i, mainly intended to protect the curtains from breaching fire; it is low and too narrow for artillery; its parapet serves merely to allow infantry, in case of a successful attack, to sweep the lunette with ditch fire. Beyond the ditch lies the covered way n o p, bounded on the inner side by the ditch and on the outer side by the interior slope of the glacis r r r, which slopes very gently down towards the field from its highest innermost edge, or crest (crête). The crest of the glacis is, again, 3 or more feet lower than the ravelin, so that all the guns of the fortress can fire over it. In these earthworks the exterior slope of the core enclosure and of the outworks within the ditch (escarp) and the outer slope of the ditch (downwards from the covered way), i.e. the counterscarp, are generally faced with masonry. The salient and re-entering angles of the covered way form large, roomy and protected points called places of arms; they are designated according to the angles at which they lie as salient (o) or re-entering (n p). To protect the covered way from enfilade fire, traverses or parapets are erected across it at intervals, leaving only narrow passages open at their ends close to the glacis. Sometimes a small work is constructed to cover the communication from the tenaille through the ditch to the ravelin; it is called a caponnière and consists of a narrow passage, covered on both sides by a parapet which slopes away outwards like a glacis. Figure 1 shows such a caponnière between the tenaille g h i and the ravelin k l m.

The section in Fig. 2 is intended to serve for the better explanation of this description. A is the rampart walk of the fortress core, B is the parapet, C is the masonry revetment of the escarp, D the ditch, E the cunette, a narrower and deeper ditch in the middle of the larger one, F the masonry revetment of the counter-scarp, G the covered way, H the glacis. The steps behind the parapet and the glacis are called banquettes and serve the infantry as a firing step, to stand upon them and fire over the protecting parapet. From the ground plan one will easily see that the guns positioned on the flanks of the bastions sweep the entire ditch in front of the adjoining bastions.

Thus the face
a' b'
is covered by the fire of the flank
c" e"
and the face
a' c'
by the fire of the flank
b d.
On the other hand, the inner faces of the two adjoining bastions cover the faces of the ravelin between them, by keeping the ditch in front of the ravelin under fire. In this manner every section of ditch is covered by flanking fire; in this consists the truly great step forward by which the bastion system inaugurates a new epoch in the history of fortification.

The inventor of the bastions is not known, and it is also not known exactly when they appeared; all that is certain is that they were invented in Italy and that Sanmicheli built two bastions on the rampart of Verona in 1527. All statements concerning earlier bastion fortifications are to be doubted. The systems of bastion fortification group themselves into several national schools; the one that first introduced the bastions, the Italian, must naturally be mentioned first. The earliest Italian bastions still bore the stamp of their origin; they were nothing other than polygonal towers or roundels and changed scarcely anything in the earlier character of the fortifications, apart from the flanking fire. The enceinte remained a stone rampart, exposed to the direct fire of the enemy; the earth rampart thrown up behind it served mainly to create space for deploying and serving the artillery, and its inner scarp was, as in the old town ramparts, likewise revetted with masonry. Only later was the parapet built of earthworks, but even at this time its entire exterior scarp was revetted with masonry up to the top, exposed to the direct fire of the enemy. The curtains were very long, between 300 and 550 yards. The bastions were very small, the size of large roundels, the flanks always perpendicular to the curtains. Now, since it is a rule in fortification that the best flanking fire always comes from a line that is perpendicular to the line to be flanked, it is obvious that the chief purpose of the old Italian flank was not the covering of the short and more distant face of the adjoining bastion, but of the long, straight line of the curtain. If the curtain became too long, a flat, obtuse-angled bastion was erected in its centre, called a platform (piata forma). The flanks were not built on the shoulder point, but set back somewhat behind the rampart of the faces, so that the shoulder points projected in order to be able to cover the flanks; each flank had two batteries, a low-standing one as well as a higher one drawn back a little, and sometimes even a casemate in the flank escarp on the bottom of the ditch. Add a ditch, and one has the entire original Italian system; there were no ravelins, no tenailles, no covered way, no glacis. But this system was soon improved. The curtains were shortened, the bastions enlarged. The length of the inner side of the polygon (
f ' f "
, Fig. 1) was fixed at 250 to 300 yards. The flanks were lengthened, amounting to one-sixth of the side of the polygon and one-quarter of the length of the curtain. As a result, greater protection was now afforded to the face of the next bastion, although the flanks still stood perpendicular to the curtain and, as we shall see, had other defects. The bastions were filled up, and in their centre a cavalier was often erected, that is, a work with faces and flanks, parallel to those of the bastion, but whose rampart and parapet were higher by so much that one could fire from the cavalier over the parapet of the bastion. The ditch was very wide and deep, the counter-scarp generally ran parallel to the face of the bastion; but because this course made the counter-scarp obstruct the part of the flank nearest the shoulder in sighting and flanking the entire ditch, the disadvantages were removed by laying out the counter-scarp in such a way that its prolongation passed through the shoulder point of the adjoining bastion. Then the covered way was introduced (first in the Milan citadel in the second quarter of the
16th century, first described by Tartaglia in 1554). It was the assembly point for the troops on a sortie as well as the place to which they withdrew; and one can say that since the introduction of the covered way, offensive movements in the defence of a fortress were applied scientifically and effectively. To increase its value, places of arms were laid out, which created more space and whose re-entrant angles also allowed good flanking fire for the covered way. To make penetration into the covered way still more difficult, rows of palisades were erected on the glacis, one or two yards from its crest; in this position, however, they were quickly destroyed by enemy fire: for this reason, from the middle of the 17th century, at the urging of the Frenchman Maudin, they were placed on the covered way, protected by the glacis. The gates lay in the centre of the curtain; for their protection a half-moon-shaped work was built in the middle of the ditch in front of them; but for the same reason that the towers were transformed into bastions, the half-moon (demilune) was soon changed into a triangular work, the present-day ravelin. It was still very small, but it was built larger when it had been found that it served not only as a bridgehead, but also covered the flanks and curtains against enemy fire, made a crossfire possible before the capitals of the bastions, and effectively flanked the covered way. The ravelins, however, were still built very small, so that the prolongation of their faces reached the fortress core at the curtain point (the outermost point of the curtain). The chief defects of the Italian school of fortification were the following:

1. The bad position of the flank. After the introduction of ravelins and covered ways, the curtain became ever rarer as a point of attack; now the bastion faces were principally attacked. To cover these well, the prolongation of the faces would have had to strike exactly the point of the curtain where the flank of the next bastion was built, and this flank would have had to be perpendicular or nearly perpendicular to this prolonged line (called the line of defence). In this case, an effective flanking trace would have been possible along the entire ditch and the front of the bastion. But the line of defence was neither perpendicular to the flanks, nor did it meet the curtain at the curtain point; it cut the curtain at a quarter, a third, or half of its length. Thus the direct flanking fire could do more harm to the garrison of the opposite flank than to the assailants of the next bastion.

2. There was an evident lack of reserves for a prolonged defence, once the main enceinte had been breached and successfully attacked at a single point.

3. The small ravelins only incompletely covered the curtains and flanks and received only a meagre flanking fire from them.

4. The great elevation of the rampart, which was entirely framed or revetted with masonry, exposed a masonry wall 15 to 20 feet high to the direct fire of the enemy in most cases, and naturally this masonry was soon destroyed. We shall see that it took almost two centuries to eradicate this prejudice in favour of uncovered masonry, even after its uselessness had been proved in the Netherlands. The best engineers and writers of the Italian school were: Sanmicheli (died 1559), he fortified Napoli di Romania in Greece as well as Candia and built the castle Lido near Venice; Tartaglia (c. 1550); Alghisi da Carpi, Girolamo Maggi and Giacomo Castrioto, who all wrote on fortification around the end of the 16th century. Paciotto from Urbino built the citadels of Turin and Antwerp (1560–1570). The later Italian authors of works on fortification, Marchi, Busca, Floriani, Rossetti, brought many improvements, yet none of them was really new. The Italians were merely more or less skilful plagiarists; they copied the greater part of their plans from the German Daniel Speckle and the rest from the Netherlanders. They all worked in the 17th century and were completely overshadowed by the rapid development in fortification science at that time in Germany, the Netherlands and France.

The deficiencies of the Italian fortification system were soon exposed in Germany. The first to point out the chief defect of the older Italian school, the small bastions and the long curtains, was the German engineer Franz, who fortified the city of Antwerp for Charles V. In the assembly that deliberated on his plan, he insisted on larger bastions and shorter curtains, but was outvoted by the Duke of Alba and the other Spanish generals, who trusted only the routine of the old Italian system. Other German fortresses distinguished themselves by adopting the casemated galleries according to Dürer's principle, e.g. Küstrin, fortified 1537–1558, and Jülich, fortified a few years later by an engineer who was known under the name Master Johann. <Master Johann: in the "New American Cyclopædia" German and English>

The man, however, who first completely broke the fetters of the Italian school and laid down the principles on which all later systems of bastion fortification are based, was Daniel Speckle, an engineer of the city of Strassburg (died 1589). His main principles were:

1. A fortress becomes stronger the more sides the polygon forming the main enceinte has, since the various fronts can thereby better support each other; consequently, the more the outer line to be defended approaches a straight line, the better. This principle, demonstrated by Cormontaigne with great expenditure of mathematical learning as his own discovery, was thus well known to Speckle 150 years earlier.

2. Acute-angled bastions are bad, likewise obtuse-angled ones; the salient angle should be a right angle. Although his rejection of acute salient angles was correct (the smallest permissible salient angle is now generally fixed at 60 degrees), the partiality of his time for right salient angles caused him to reject obtuse ones, which in reality are very advantageous and are unavoidable in polygons with many sides. This indeed seems to have been merely a concession to the prejudices of his epoch, for the ground plans of what he considered his strongest manner of fortification all have obtuse-angled bastions.

3. The Italian bastions are much too small; a bastion must be large. Speckle's bastions are consequently larger than Cormontaigne's.

4. Cavaliers are necessary in every bastion and on every curtain. This corresponded to the siege method of his time, in which high cavaliers in the trenches played a great role. But according to Speckle’s intention the cavaliers were to achieve more than withstanding the cavaliers in the trenches; they are real coupures, which were already prepared beforehand in the bastion and, once the core rampart was breached and stormed, formed a second line of defence. The entire merit, generally attributed to Vauban and Cormontaigne, of having built cavaliers as permanent coupures, therefore in reality belongs to Speckle.

5. At least a part of the flank, or better still the entire flank of a bastion, must stand perpendicular to the line of defence, and the flank be erected at the point where the line of defence crosses the curtain. This important principle, the alleged discovery of which constitutes the greater part of the fame of the French engineer Pagan, was thus publicly set forth 70 years before Pagan.

6. Casemated galleries are necessary for the defence of the ditch; accordingly in Speckle they are found on the faces and flanks of the bastion, but only for infantry; had he made them large enough for artillery, he would in this respect have been completely up to the latest state of development.

7. To be of use, the ravelin must be as large as possible; hence Speckle’s ravelin is the largest ever proposed. Now, Vauban’s improvements on Pagan’s system consist partly, and Cormontaigne’s improvements on Vauban’s system almost entirely, in the successive enlargement of the ravelin; but Speckle’s ravelin is a good deal larger than even Cormontaigne’s.

8. The covered way must be made as strong as possible; Speckle was the first to see the immense importance of the covered way and strengthened it accordingly. The crests of the glacis and of the counterscarp were formed en crémaillère (like the teeth of a saw) in order to render enfilade fire ineffective. Once again Cormontaigne took up this idea of Speckle; but he retained the traverses (short ramparts against enfilade fire thrown across the covered way), which Speckle rejected. Modern engineers have generally come to the conclusion that Speckle’s plan is better than Cormontaigne’s. Moreover, Speckle was the first to place artillery on the places of arms of the covered way.

9. No piece of masonry may be exposed to the view and the direct fire of the enemy, so that his breaching batteries cannot be employed until he has reached the crest of the glacis. This most important principle was not generally adopted before Cormontaigne, although it had been laid down by Speckle in the 16th century; even Vauban exposes a great part of his masonry (see C, Figure 2).

In this brief outline of Speckle’s ideas, the fundamental principles of all modern bastioned fortification are not only contained but clearly set forth, and his system, which would even today offer very good defensive works, is truly magnificent when one considers in what age he lived. There is not a single famous engineer in the whole history of the modern art of fortification who cannot be shown to have borrowed some of his best ideas from this great, unique source of bastioned defence. Speckle’s practical abilities as a military architect were demonstrated in the construction of the fortresses of Ingolstadt, Schlettstadt, Hagenau, Ulm, Colmar, Basel and Strasbourg, all of which were built under his direction.

At about the same time, the struggle for the independence of the Netherlands produced another school of fortification. The Dutch towns, from whose old ramparts no resistance to a formal attack could be expected, had to be fortified against the Spaniards; however, there was neither time nor money for the erection of the high masonry bastions and cavaliers of the Italian system. But the nature of the soil, through its slight elevation above sea level, offered other resources, and therefore the Dutch, masters of canal and dyke construction, relied on water in their defence. Their system was the exact opposite of the Italian: wide and shallow wet ditches, 14 to 40 yards wide; low earth ramparts without any masonry revetment, but covered by an even lower advanced earth rampart (fausse-braye) for the stronger defence of the ditch; numerous outworks in the ditch, such as ravelins, demi-lunes (ravelins before the salient angle of the bastion), hornworks and crownworks
(1)
; and, finally, a better utilisation of the terrain than by the Italians. The first town fortified exclusively with earthworks and water ditches was Breda (1533). Later the Dutch system underwent some improvements: a narrow strip of the scarp was revetted with masonry, since the water ditches, when frozen over in winter, were easily crossed by the enemy; sluices and locks were installed in the ditch to let in the water at the moment when the enemy had begun to sap the hitherto dry bottom; and finally, locks and dams were built for a systematic inundation of the terrain around the foot of the glacis. On this older Dutch system of fortification wrote Marobis (1627), Freitag (1630), Völker (1666) and Melder (1670). Scheither, Neubauer, Heidemann and Heer (Germans, from 1670-1690) attempted to apply Speckle’s principles to the Dutch system.

Of all the different schools of fortification, the French has enjoyed the greatest popularity; its principles have found practical application in a greater number of still existing fortresses than those of all other schools put together. Nevertheless, no school is so poor in ideas of its own. There is nothing in the whole French school, neither a new work nor a new principle, that is not borrowed from the Italians, the Dutch, or the Germans. But the great merit of the French is to have reduced the art of fortification to exact mathematical rules, to have shaped the proportions of the various lines symmetrically, and to have applied scientific theory to the differing conditions of the place to be fortified. Errard of Bar-le-Duc (1594), commonly called the father of French fortification, has no claim to this designation; his flanks form an acute angle with the curtain, making them even more ineffective than those of the Italians. More important is Pagan (1645). He was the first to introduce and popularise in France Speckle’s principle that the flanks must be perpendicular to the lines of defence. His bastions are spacious; the proportions between the lengths of the faces, flanks and curtains are very good; the lines of defence are never longer than 240 yards, so that the whole ditch, but not the covered way, lies within musket range from the flanks. His ravelin is larger than that of the Italians and has a redoubt, or smaller ravelin, in its gorge, so as still to be able to offer resistance once the rampart has already been taken. Pagan covers the faces of the bastions with a narrow detached work in the ditch, called a counterguard, a work already used by the Dutch (the German Dillich appears to have introduced it first). The bastions have a double rampart on the faces, the second serving as a coupure; but the ditch between the two ramparts is entirely without flanking fire. The man who made the French school the first in Europe was Vauban (1633-1707), Marshal of France. Although his actual military fame rests on his two great inventions for the attack on fortresses (ricochet fire and parallels), he is better known to the public as a builder of fortresses. What we have said of the French school applies to a high degree to Vauban’s system. In his constructions we see as great a variety of forms as can be reconciled with the bastioned system; but there is nothing new among them; still less does he attempt to adopt forms other than bastioned ones. The

arrangement of the details, the proportions of the lines, the profiles and the application of theory to the ever-varying local conditions are, however, so ingenious that they appear perfect in comparison with the works of his predecessors, so that since Vauban one can speak of a scientific and systematic art of fortification. He wrote, however, not a single line about his system of fortification, but from the great number of fortresses built by him the French engineers have attempted to derive the theoretical rules that served him as a guide, and thus three manners were set up, called Vauban’s first, second and third manner. Figure 1 shows the first manner very simplified. The principal dimensions were: The exterior side of the polygon, from the point of one bastion to that of the next, was 300 yards (on average); in the middle of this line a perpendicular
a b
was erected, one-sixth of the former; through
b
ran the lines of defence from
a″
and
a′, a″ d′
and
a′ e″
. From the points
a″
and
a′
two-sevenths of the line
a″ a′
transferred onto the lines of defence give the faces
a″ c″
and
a′ b′
. Around the shoulder points
c″
and
b′
circular arcs were drawn with the radius
c″ d′
or
b′ e″
between the lines of defence, thus obtaining the flanks
b′ d′
and
c″ e″
. The line
e″ d′
is the curtain,

The ditch: A circular arc before the bastion point with a radius of 30 yards, extended by the tangents drawn from the shoulder points of the adjacent bastions to this circular arc, gives the counterscarp. The ravelin: About the curtain point
e″
a circular arc
g d
with the radius
e″
g
(
g
is a point on the opposite face, 11 yards behind the shoulder point) drawn until it intersects the extension of the perpendicular
a b
, gives the point of the ravelin; the chord of the arc just described gives the face, which is continued from the ravelin point until it meets the extension of the tangent that forms the counterscarp of the main ditch; the gorge of the ravelin is likewise determined by this tangent, so that the entire ditch remains open for the fire of the flanks. Before the curtain, and only there, Vauban retained the Dutch fausse-braye; the Italian Floriani had already done this before him, and the new work was called tenaille (tenaglia). Its faces ran in the direction of the lines of defence. The ditch before the ravelin was 24 yards wide, the counterscarp parallel to the ravelin faces and the point rounded off.

In this way Vauban obtained spacious bastions, and his flanked, salient angles remained entirely within musket range; the simplicity of these bastions, however, makes the defence of the place

impossible as soon as the face of a bastion has been breached. Vauban’s flanks, which form an acute angle with the lines of defence, are not as good as those of Speckle or Pagan; but he abolished the two or three terraced tiers of unprotected guns which were present on most flanks of the Italian and the early French school and were never very advantageous. The tenaille is intended to strengthen the defence of the ditch by infantry fire and to protect the curtain from direct breaching fire from the crest of the glacis; but this is achieved only very imperfectly, since breaching batteries on the re-entrant place of arms (n, Figure 1) have a full view of the piece of curtain adjoining the flank at e. Therein lies a great weakness, since a breach there would encompass all the coupures that have been prepared in the bastion as a second line of defence. The fault lies with the still too small ravelin. The covered way, not with cremaillères but with traverses, is far weaker than that of Speckle; the traverses prevent not only the enemy but also the defence from enfilading the covered way. The communications between the individual works are generally good, but are still insufficient for vigorous sorties. The profiles are of a strength that remains in general use today. But Vauban still clung to the system of revetting the whole exterior of the rampart with masonry, so that the masonry was exposed to a height of at least 15 feet. This error was committed in many of Vauban’s fortresses, and once made it can only be remedied at great expense by widening the ditch in front of the bastion faces and erecting counterguards of earthwork to cover the masonry. For a great part of his life Vauban held to his first manner; but after 1680 he introduced two further manners intended to permit a longer defence once a breach had been made in the bastion. To this end he reverted to an idea of Castrioto, who had proposed modernizing the old tower and rampart fortification by detached bastions placed in isolation in the ditch in front of the towers. Vauban’s second and third manners agree with this. In addition he enlarged the ravelin; the masonry is somewhat better covered; the towers are casemated, but poorly; the fault that a breach can be made in the curtain between the bastion and the tenaille remains and renders the detached bastion partly worthless. Nevertheless Vauban considered his second and third manners very strong. When he handed Louis XIV the plan for the fortification of Landau (second manner), he said: “Sire, here is a place which all my art would not suffice to conquer.” This did not prevent Landau from being taken three times during Vauban’s lifetime (1702, 1703 and 1704) and once more shortly after his death (1713).

Vauban’s errors were corrected by Cormontaigne, whose manner can be regarded as the most accomplished of the bastionary system. Cormontaigne (1696-1752) was general of the engineers. His larger bastions allowed the construction of permanent coupures and second lines of defence; his ravelins were almost as large as Speckle’s and completely covered the part of the curtain that Vauban had left uncovered. In polygons of 8 or more sides, his ravelins were sited so far forward that, from the ravelins adjacent to the attacked bastion, the works of the besiegers could be taken in reverse as soon as the latter had reached the crest of the glacis. To prevent this, two ravelins must be taken before a breach can be made in a bastion. The mutual support of the large ravelins becomes more effective the more the line to be defended approaches a straight line. The re-entrant place of arms was reinforced by a redoubt. The crest of the glacis is laid out en crémaillère as in Speckle, but the traverses have been retained. The profiles are very good, and the masonry is always covered by earthworks placed in front of it. With Cormontaigne the French school concludes, as far as the construction of bastionary defences with outworks within the ditch is concerned. A comparison of the progressive development of bastionary fortification from 1600 to 1750 and its final results laid down by Cormontaigne with the principles of Speckle explained above will help to place in its proper light the magnificent genius of the German engineer; for although the outworks in the ditch were greatly increased, during that entire 150 years not a single important principle was discovered that had not already been clearly and distinctly demonstrated by Speckle.

After Cormontaigne, the engineering school of Mézières (around 1760) made some insignificant changes in his manner, which mainly represent a return to the old rule of Speckle that the flanks must stand at right angles to the lines of defence. But the school of Mézières is above all remarkable because it builds outworks beyond the covered way for the first time. On fronts that were particularly endangered in an attack, it erects on the capital of the bastion at the foot of the glacis a detached ravelin, called a lunette, and thus approaches for the first time the modern system of permanently entrenched camps. At the beginning of the 19th century, Bousmard, a French émigré who served in Prussia and was killed in Danzig in 1807, also tried to improve on Cormontaigne; his ideas are rather complicated, and the most notable thing about them is that his very large ravelin is pushed forward almost to the foot of the glacis, so that to a certain degree it takes the place and the functions of the lunette just described.

A Dutch engineer of Vauban’s time, who opposed him more than once with honour in siege warfare, Baron Coehoorn, further developed the old Dutch system of fortification. His manner offers a stronger defence than even that of Cormontaigne, by virtue of the clever combination of wet and dry ditches, the great facilities for sorties, the excellent communications between the works, and the ingenious redoubts and coupures in his ravelins and bastions. Coehoorn, a great admirer of Speckle, is the only engineer of repute who was honest enough to acknowledge how much he owed him.

We have seen that even before the introduction of bastions Albrecht Dürer employed caponnières to allow stronger flanking fire. In his fortified quadrilateral he relied for the defence of the ditch entirely on these caponnières; there are no towers at the corner of the fort; it is a simple quadrilateral having only salient angles. From the effort to make the enceinte of a polygon coincide completely with its exterior outline, so that only salient and no re-entrant angles occur, and to flank the ditch by caponnières, there developed the so-called polygonal fortification, of which Dürer must be considered the father. A star-shaped enceinte, on the other hand, in which salient and re-entrant angles regularly alternate and in which each line is simultaneously flank and face, since it flanks the ditch of the next line with the segment adjoining the re-entrant angle and commands the terrain with the segment nearest the salient angle—such an exterior outline gives the tenaille fortification. The older Italian school and various representatives of the older German school had proposed this form, but it was developed only later. The system of Georg Rimpler (engineer to the German Emperor, killed during the defence of Vienna against the Turks in 1683) forms a kind of intermediate stage between the bastionary and the tenaille systems. What he calls middle bulwarks (Mittelbollwerke) is in reality a complete line of tenailles. He declared himself energetically against open batteries, simply provided with a parapet, and insisted on casemated batteries wherever they could be erected; on the flanks, in particular, two or three storeys of well-covered guns would have a far greater effect than two or three terraced tiers of guns in open flank batteries, which could never fire simultaneously. He also insisted on batteries, that is redoubts, in the places of arms of the covered way, which Coehoorn and Cormontaigne adopted, and particularly on a double and triple line of defence behind the salient angles of the enceinte. In this respect his system is remarkably ahead of its time; his whole enceinte consists of independent forts, each of which has to be conquered individually, and large defensive casemates are used in a manner that reminds us in almost every detail of their application of the more recent constructions in Germany.

Montalembert’s system doubtless owed as much to Rimpler as the bastionary system of the 17th and 18th centuries owed to Speckle. The writer who first set forth in detail the advantages of the tenaille over the bastionary system was Landsberg (1712); but it would lead us too far to deal with his arguments or to describe his fortified outline. From the large number of skilful German engineers who followed Rimpler and Landsberg, we may still mention the Mecklenburg colonel Buggenhagen (1720), the inventor of blockhouse traverses or hollow traverses for casemated musket fire, and the Württemberg major Herbort (1734), the inventor of defensive barracks—large barracks in the gorge of salient works, protected against vertical fire by casemates provided with embrasures on the side facing the enceinte, and barracks and store-rooms on the side towards the town. These two constructions are now very widely used.

Thus we see that, with the sole exception of Speckle, the German school from the very beginning rejected bastions and mainly wished to replace them by tenailles, and that at the same time it attempted to introduce a better interior defence system, above all by the construction of casemated galleries, which in turn were regarded by notable French engineers as the height of absurdity.

One of the greatest engineers France ever produced, the Marquis de Montalembert (1713-1799), major-general of cavalry, however, went over with colours flying into the camp of the German school, to the great horror of the entire French engineer corps, which until

He has up to the present day vilified every word he wrote. Montalembert sharply criticised the defects of the bastionary system; the ineffectiveness of its flanking fire; the almost absolute certainty that the enemy’s shots, if they missed one line, must hit another; the inadequate protection against vertical fire; the complete uselessness of the curtain as far as fire was concerned; the impossibility of constructing good and large coupures in the throats of the bastions, proved by the fact that no fortress of his time had any of the manifold permanent coupures proposed by the theoreticians of the school; the weakness of the outworks, their poor communication and deficient mutual support. Montalembert therefore preferred either the tenaille or the polygonal system. In both cases the core enceinte consisted of a series of casemates with one or two tiers of batteries, the masonry of which was covered against direct fire by a counterguard or couvre-face of earthwork that extended all around and had a second ditch in front of it; this ditch was flanked by casemates in the re-entering angle of the couvre-face, covered by the parapet of the redoubt or lunette in the re-entering place-of-arms. The entire system was based on the principle of confronting the enemy, at the moment when he reached the crest of the glacis or the couvre-face, with such an overwhelming fire from casemated guns that it would be impossible for him to set up his breaching batteries. He insisted that this could be achieved by casemates, despite the unanimous condemnation of the French engineers; later he even combined systems of circular and tenaille fortifications, in which all earthwork was dispensed with and the entire defence was entrusted to high casemated batteries of 4 to 5 tiers, the masonry of which was to be protected solely by the fire of the batteries themselves. Thus in his circular manner he proposed to concentrate the fire of 348 cannon on any point 500 yards from the fortress, and expected that such an immense superiority of fire would render the erection of siege batteries altogether impossible. In this, however, he found no adherents, except in the arrangement of the sea fronts of coastal forts; here it was demonstrated very clearly by the bombardment of Sevastopol that ships’ guns could not effect a breach in strong casemated ramparts. The excellent forts of Sevastopol, Kronstadt, Cherbourg, and the new batteries at the harbour entrance of Portsmouth (England), as well as almost all modern forts for harbour defence against warships, are built on Montalembert’s principle.

The partly uncovered masonry of the Maximilian towers at Linz (Austria) and of the redoubts in the detached forts of Cologne are modelled on less fortunate projects of Montalembert. Uncovered masonry forts have also sometimes been adopted in the fortification of steep heights (e.g., Ehrenbreitstein in Prussia), but practice must decide what resistance they are capable of.

The tenaille system has, as far as we know, never been used in practice, but the polygonal system is much favoured in Germany; there most modern works are built according to it, whereas the French persistently adhere to the bastions of Cormontaigne. In the polygonal system, the enceinte is usually a simple earthen rampart with revetted scarp and counterscarp, with large caponiers in the centre of the forts and with large defensive barracks behind the rampart and covered by it, to serve as coupures. Similar defensive barracks have also been erected as coupures in many bastionary works, to close the throats of the bastions; the rampart serves as a counterguard to protect the masonry from long-range fire.

Of all Montalembert’s proposals, however, that of detached forts has had the greatest success and opened a new era not only in the art of fortification but also in the siege and defence of fortresses, and in warfare in general. Montalembert proposed to surround large fortresses at important points with a single or double chain of small forts on commanding heights; although the forts are apparently isolated, they can support each other with their fire, and as they facilitate large sorties, they can make a bombardment of the place impossible and, if necessary, form an entrenched camp for an army. Vauban had already introduced permanent entrenched camps under the guns of fortresses, but these entrenchments consisted of long, continuous lines which, if broken through at only one point, were completely at the mercy of the enemy. But Montalembert’s entrenched camps could offer much stronger resistance, for each fort had to be taken singly, and no enemy could open his approaches against the place until at least 3 or 4 of the forts were captured. Moreover, the siege of any fort could at any time be interrupted by the garrison, or rather by the army encamped behind the forts; thus a combination of open-field fighting with regular fortress warfare was secured, which must greatly strengthen the defence.

When Napoleon led his armies hundreds of miles through enemy country without ever paying attention to the fortresses, all of which had been built according to the old system, and when, on the other hand, the Allies (1814 and 1815) marched straight on Paris, leaving almost unnoticed behind them the triple belt of fortresses with which Vauban had furnished France, it became obvious that a system of fortification was obsolete which confined its outworks to the main ditch or at most to the foot of the glacis. Such fortresses had lost their power of attraction in the face of the large armies of modern times. Their means of inflicting damage did not exceed the range of their guns. It became necessary, therefore, to find new means of impeding the impetuous movements of modern invading armies, and Montalembert’s detached forts were applied on a large scale. Cologne, Koblenz, Mainz, Rastatt, Ulm, Königsberg, Posen, Linz, Peschiera, and Verona were converted especially into large entrenched camps capable of holding 60,000 to 100,000 men, but which, in case of need, could also be defended by much smaller garrisons. At the same time, the tactical advantages of the place to be fortified were relegated to the background by the strategic considerations that now determined the location of fortresses. Only such places were fortified as were able, directly or indirectly, to resist the advance of a victorious army and which, being large towns, offered the army great advantages as centres of the resources of whole provinces.

The situation on large rivers, especially where two important rivers meet, was favoured, as it forced the attacking army to divide its forces. The enceinte was simplified as much as possible, and the outworks in the ditch were almost entirely abolished; it sufficed to secure the rampart against a non-formal attack. The main field of struggle lay around the detached forts, and these were defended not so much by the fire of their ramparts as by the sorties of the fortress garrison itself. The largest fortress built on this plan is Paris; it has a simple bastioned enceinte with bastioned forts, almost all square; in the whole fortification there is no outwork, not even a ravelin. Without doubt, the defensive strength of France has increased by 30 per cent through this new and immense entrenched camp; it is large enough to afford refuge to three defeated armies. The actual value of the various methods of fortification has, through this improvement, lost much of its significance, the cheapest will now be the best; for the defence

is no longer based on the passive system of waiting for the enemy behind the ramparts until he opens his approaches and then firing on them with cannon, but on active defence, which takes the offensive with the concentrated strength of the garrison against the necessarily divided forces of the besieger.

II. Siege

The art of siege warfare was brought to a certain perfection by the Greeks and Romans. They attempted to break the walls of fortresses with the battering-ram and approached them under cover of heavily roofed galleries or, if necessary, of a high structure which, by its greater height, commanded the ramparts and towers and was to secure the approach of the assault columns. The invention of gunpowder did away with these arrangements; fortresses now had lower ramparts, but fire was effective at long distances; the fortress was approached by trenches, which ran in zigzag or curved lines towards the glacis; batteries were erected at various points to silence as far as possible the fire of the besieged and to demolish their masonry. Once the crest of the glacis was reached, a high trench cavalier was erected to command the bastions and their cavaliers and then to complete the breach by breaching fire and to prepare the assault. The curtain was the point principally attacked.

For this mode of attack there was, however, no system until Vauban introduced parallels with ricochet fire and regulated the process of siege in the manner which is still authoritative today and which is still called Vauban’s attack. The besieger invests the fortress on all sides with sufficient forces, selects the fronts to be attacked, and opens at night, about 600 yards from the fortress, the first parallel (all siege works are carried out mainly at night). A trench parallel to the sides of the besieged polygon is drawn around at least three of these sides and fronts; the earth thrown up on the side facing the enemy and supported on the sides of the trench by gabions (wicker baskets filled with earth) forms a sort of parapet against the fire of the fortress. In this first parallel the ricochet batteries are erected, to enfilade the long lines of the attacked fronts.

If we take a bastioned hexagon as the object of the siege, ricochet batteries should be provided – one for each face – to enfilade the faces of 2 bastions and 3 ravelins. These batteries direct their fire so that it just passes over the parapet of the works, rakes the faces lengthwise and endangers guns as well as men. Similar batteries are erected to enfilade the branches of the covered way, and mortars and howitzers are placed in batteries to shell the interior of the bastions and ravelins with shells. All these batteries are covered by parapets of earthwork. At the same time, zigzag trenches are pushed forward against the place at two or more points, which are intended to protect against any enfilade fire from the town; and as soon as the fire of the fortress begins to slacken, the second parallel is opened at about 350 yards from the works. In this parallel the dismounting batteries are erected. They serve for the complete destruction of the artillery and the embrasures on the faces of the fortress; 8 faces are to be attacked (2 bastions and their ravelins as well as the inner faces of the adjoining ravelins), for each of which a battery is laid out parallel to the attacked faces, and each embrasure is exactly opposite an embrasure of the fortress. From the second parallel, zigzags are again pushed forward against the town; at 200 yards the half-parallel is built, which forms an extension of the zigzags and is furnished with mortar batteries, and finally the third parallel is opened at the foot of the glacis. This is furnished with heavy mortar batteries. By this time the fire of the place will have been almost silenced, and the approaches – in winding or angular lines, to escape the ricochet fire – are carried forward to the crest of the glacis, which is reached opposite the salients of the two bastions and the ravelin. Then, in the salient place-of-arms, a lodgement or a trench and parapet is laid out to enfilade the ditch by infantry fire. If the enemy ventures energetic and bold sorties, a fourth parallel becomes necessary, linking the salient places-of-arms across the glacis. In the other case, a sap is pushed forward from the third parallel to the re-entrant places-of-arms and the crowning of the glacis, or the construction of a trench along the covered way on the crest of the glacis is completed. Then, in this *couronnement*, the counter-batteries are erected to silence the fire of the flanks that sweeps the ditch, and afterwards the breaching batteries, which are directed against the salient and the faces of the bastions and of the ravelin. Opposite the points where a breach is to be made, a mine gallery is dug, leading from the trenches through the glacis and the counterscarp down into the ditch; the counterscarp is breached and a new trench is carried through the ditch to the foot of the breach; the side exposed to the enfilade fire of the flank is covered by a parapet. As soon as the breach and the passage of the ditch are completed, the assault begins.

This applies to a dry ditch; across a wet ditch a causeway of fascines must be built, likewise covered by a parapet on the side of the adjoining bastion flank. If, after the capture of the bastion, it turns out that behind it there is another trench or a coupure, a lodgement must be erected, new batteries must be established at the breach, a new breach must be made, a new descent into the ditch and a new passage across it must be built, and a new assault must be undertaken. The average resistance of a hexagon fortified according to Vauban’s first manner against such a siege is calculated at 19 to 22 days if no coupures are present, and 27 or 28 days if it is provided with coupures. Cormontaigne’s manner is supposed to hold out 25 and 35 to 37 days respectively.

III. Field Fortification

The construction of fieldworks is as old as armies themselves. In antiquity people were far more experienced in this art than in our modern armies; the Roman legions, when they faced the enemy, entrenched their camp every night. During the 17th and 18th centuries, field fortifications were also very widespread; and in the wars of Frederick the Great, the field guards on outpost duty usually threw up lightly profiled redans. Yet even then, and still more today, the construction of field fortifications was, and is, limited to the strengthening of a few positions selected beforehand with a view to certain eventualities during a campaign, for example Frederick the Great’s camp at Bunzelwitz, Wellington’s lines at Torres Vedras, the French lines of Weissenburg and the Austrian trenches before Verona. Under such circumstances, field fortifications can significantly influence the outcome of a campaign, for they enable a numerically weaker army to offer successful resistance to a superior one. Formerly, the entrenched lines were continuous, as in Vauban’s permanently fortified camps; but because of the disadvantage that the entire line was useless if it was broken through and captured at one point, they now generally consist of one or more lines of detached redoubts, which flank one another by their fire and allow the army to fall upon the enemy through the gaps as soon as the fire of the redoubts has broken the force of his attack. That is the principal purpose of field fortifications; but they are also used individually, as bridgeheads, to defend the approach to a bridge, or to close an important pass to small detachments of the enemy. Apart from all the more fanciful forms of works, which are no longer appropriate today, such fortifications should consist of works that are open or closed at the gorge. The former will be either redans (two parapets with a ditch in front, forming an angle facing the enemy) or lunettes (redans with short flanks). The latter may be closed at the gorge by palisades. The principal closed fieldwork still in use today is the quadrilateral redoubt, a regular or irregular quadrilateral, enclosed on all sides by a ditch and a parapet. The parapet is as high as that of permanent fortification (7 to 8 feet high), but not as thick, because it has to resist only field artillery. Since none of these works has its own flanking fire, they must be laid out so that they flank one another within range of musketry fire. In order to carry this out effectively and to strengthen the whole line, the method has now become generally accepted of forming an entrenched camp by a line of quadrilateral, mutually flanking redoubts, with a line of simple redans lying in front of the intervals between the redoubts. Such a camp was built in 1849 before Komorn south of the Danube and was defended by the Hungarians for two days against a far superior army.

Footnotes by Frederick Engels

(1)
A hornwork is a bastioned front – two half bastions, a curtain, and a ravelin – advanced into the main ditch and closed on each side by a straight line of rampart and ditch which is aligned on the bastion faces of the enceinte so as to be completely flanked by the latter’s fire.

A crownwork consists of two such advanced fronts (one bastion flanked by two half bastions), a double crownwork has three fronts.

In all these works the rampart must be lower at least by as much as the difference in height between the enceinte and the rampart of the ravelin, so that both can be commanded from the enceinte. The laying out of such outworks, which were of course exceptions, was governed by the nature of the ground.