Damsare generally made of earth, but sometimes of other materials, as occasion may require: their use is to confine water.
Flêchea work consisting of two faces,terminating in a saliant angle of 90°, the faces are generally 75, or 80 feet long, the parapet 6 feet thick, and the ditch 7 feet broad.
Forts, in field fortification, are of various sorts, viz.
Field fortsmay be divided into two kinds: the one defending itself on all sides, as being entirely surrounded; the other, bordering on a river, &c. remain open at the gorge. They have the advantage of redoubts, in being flanked, and the disadvantage in containing less within, in proportion to their extent.
Star fortsare so called, because they resemble that figure. They were commonly made of 4 angles, sometimes of 5, and very rarely of 6; but we find them now made of 7 and 8 angles. Let their figure however, be what it will, their angles should be equal; if formed of equilateral triangles, so much the better; for then the flanking angle being 120°, the fires cross better and nearer; and as the 2 flanks are on the same line, the space not defended before the saliant angle, is reduced to a parallelogram, whose smallest side is equal to the gorge.
Bastioned fortsdiffer in nothing from that of places, except that the figure is less, and the attack supposed of another kind. It is reckoned sufficient to flank them with half bastions.
Triangular forts.As these kind offortscontain less in proportion than any other, they are consequently used as seldom as possible.
Square fortsare in many respects preferable to the triangular ones. SeeFort.
Lines, in field fortification, are of several sorts, viz. the front of a fortification, or any other field work, which with regard to the defence, is a collection of lines, contrived so as reciprocally to flank each other.
Lines of intrenchmentare made to cover an army; or a place indifferently fortified, and which sometimes contains the principal magazine of an army; or to cover a considerable extent of ground, to prevent an enemy from entering into the country to raise contributions, &c.
Lines, of whatever form or shape, should be every where equally strong, and alike guarded.
Maxims.1st. To inclose with the work as much ground as possible, having regard to circumstances. This attention chiefly concerns redoubts and small works.
2d. If there are several works near each other, their lines of defence should be so directed, as to defend each other without being annoyed by their own fire.
3d. Not to depend on the defence of small arms, but where they can fire at right angles; as they too generally fire without aim, and directly before them.
4th. Not to have recourse to the 2d flank or fire of the curtain, but when there is an absolute necessity.
5th. That the flanking angle be always a right one, or at least obtuse, but never to exceed 100°, if possible, there being no fear here, as in a fortification, of the flank being too much exposed. Besides, it is not necessary to graze the faces, or even to fire obliquely on them; since there is no danger of being exposed to the defence of a breach, or lodgment of the miners. The only thing to apprehend, is a sudden attack.
6th. That the flanking parts be sufficiently extended, so that the interior of their parapets at least may rake the whole breadth of the opposite ditch.
7th. Never to make an advanced ditch in dry ground, unless it can be enfiladed throughout, and under a proper angle be defended by the work which it covers, or surrounds.
8th. Not to allow more than from 60 to 80 toises for the lines of defence, when they proceed from two flanks separated by two branches, forming a saliant angle, or when not made to cross, though produced.
9th. That the parts most extended, and consequently the weakest in themselves, be as much defended as possible, and have at least the fire of two flanks, besides their own direct fire.
Redansare a sort of indented works, consisting of lines and faces, that form saliant and re-entering angles, flanking one another. Lines are often constructed with redans: their saliant angles are generally from 50 to 70°.
Indented redansare when the two faces are indented, in that case the faces of each indented angle is 8¹⁄₂ feet only.
Tambour, a kind of work formed of palisades, 10 feet long, and 6 inches thick, planted close together, and driven 2 or 3 feet into the ground; so that when finished it has the appearance of a square redoubt cut in two. Loop-holes are made 6 feet from the ground, and 3 feet asunder, for the soldiers to fire through, who are placed on scaffolds 2 feet high. They have often been used by the French with great advantage.
Têtes-de-pont.SeeBridge-heads.
Trous-de-loupare holes dug in the ground, circular at top, about 4¹⁄₂ feet diameter, and 6 feet deep, pointed at bottom, like an inverted cone, or sugar loaf. A stake six feet long is fixed in their centre, driven 2 feet into the ground, and made sharp at top. Two or three rows of them are dug chequerwise, about 6 paces from the ditch of a field-work. They prevent the approach of horse, &c.
Perpendicular Fortification.
The principles of Vauban for direct or horizontal works, are the most perfect of all others: indeed all the masters of the art in modern times, who have introduced any thing new, allow that their worksare only improvements of Vauban. The writings of Cormontagne are the most approved of the late writers on military defence. The principles of elevated works to cover naval roads and harbors, is among the improvements on Vauban; the works at Cherbourg, in France, and at fort Columbus, New York harbour, are very happy examples of the power of such works, as well as of the talents of the Engineers who erected them. Those at New York were by Col. Williams of the United States engineer corps.
SubterraneousFortification.
These consist of the different galleries and branches which lead to mines, to the chambers belonging to them, or to fougasses, and which are required whenever it is found necessary to explode for the purposes of attack or defence. A subterraneous fortification may be of a permanent or temporary construction, offensive or defensive nature. Whenever this sort of work is adopted to strengthen and secure a fortified place, it is generally built of stone or brick, and made sufficiently solid to last a long time; it is then called permanent and defensive. Any place which is put in a state to withstand the subterraneous attacks of a besieging enemy, is said to be countermined.
When the besieger wishes to make an impression on a fortification of this sort, he must first construct galleries which he covers with wood, &c. He then practices offensive and temporary fortifications of the subterraneous sort. These works are well calculated to aid him in securing a lodgment for his subterraneous artillery, and in establishing chambers, fougasses, &c.
With respect to fortification in general, different authors recommend different methods; but the principal are those of Pagan, Blondel, Vauban, Coehorn, Belidor, Scheiter, and Muller.
It must, however, be constantly recollected by every engineer, that his views are not to be confined to the mere art of fortification. He ought further to know the use which different generals, in different periods, have made of natural strength and position; without an attention of this sort, he will fall very short of that extensive knowlege, which every military man, who aims at military fame, must be ambitious of acquiring. Chains of mountains, and volumes of water, together with the influence which different climates have upon the latter element, should always constitute a part of the natural system that ought to form an essential portion of his application. Hydrography will likewise assist him in this pursuit. To enlarge upon this important branch of geography, and to point out the great means which it affords of natural defence and offence in fortification, would be to exceed the limits of our present undertaking. We shall, therefore, refer our military readers to Belair’sElemens de Fortification, and content ourselves with submitting a short account of the different authors who have either given original systems, or have greatly improved those that were already known. Independent of whom, may be named the following writers, who have likewise contributed to the general knowlege of fortification, viz. Errard, Deville, Belidor, D’Alembert, Cormontagne, Folard, Clairac, Muller, Robins, LeBlond, Didier, Marshal Saxe, Cugnot, Tielke, Landsberghen, Trincano, Fallios, Rosard, Belair, &c.
Fortification, according to the method of Pagan, consists in three different sorts, viz. the great, the mean, and little, whose principal dimensions are contained in the following
Table.
Blondel fortifies within the given polygon: he establishes two sorts of fortification; the great one, whose exterior side is 200 toises, and the lesser one 170; because he will not have the line of defence exceed 140 toises, which is the greatest musquet shot, nor less than 120 toises, not to increase the number of bastions. He begins by the diminishing angle, which may be found by taking 90 degrees from the angle of the polygon, and by adding 15 degrees to the third of the remainder.
Vauban’s method is divided into little, mean, and great: the little is chiefly used in the construction of citadels; the mean, in that of all sorts of towns; and the great, in particular cases only.
Table.
Forts.Little.Mean.Great.Side of Polygon8090100110120130140150160170180190200260Length of perpendicular101112¹⁄₂1415162021232530312522Faces of Bastions2225283033354042454750535560Capital of Ravelins2528303538404550505255556050
In the first horizontal row are the numbers expressing the lengths of the exterior sides from 80 to 260.
In the second, the perpendiculars answering to these sides.
In the third, the lengths of the faces of the bastions; and in the fourth, the lengths of the capitals of the ravelins.
Belidor’s method is divided also into little, mean, and great: and in all three the exterior side is 200 toises; the perpendicular of the little is 50, that of the mean 55, and the great 40: the faces of the first 70, the second 70, and the third 55 toises.
Scheiter’s method is divided into the great, mean, and small sort. The exterior side of the polygon for the great sort is 200 toises, the mean sort 180, and the small 160. The line of defence in the first is 140 toises, the second 130, and the third 120. This line is always rasant. All the other lines are fixed at the same length for all polygons, whose structure chiefly depends upon the knowlege of the exterior side, of the capital, or of the flanked angle, the rest being easily finished.—See theTable.
Tableof capitals and flanked Angles.
Errard, of Bois le-Duc, who was employed by Henry IV. and was the first that laid down rules in France respecting the best method of fortifying a place so as to cover its flank, constructs that flank perpendicular to the face of the bastion; but by endeavoring to cover it effectually, he makes the gorges too exiguous, the embrasures too oblique, and leaves the ditch almost defenceless.
The Chevalier de Ville, who succeeded Errard, draws the flank line perpendicular to the curtain; but here again the embrasures are too oblique, especially in the polygons, and the ditch is necessarily ill guarded. This engineer’s method of fortifying is stiled by most authors, theFrench method. His favorite maxim is to make the flank angle straight, and the flank equal to the demigorge.
Count Pagan makes the flank perpendicular to the line of defence, which method seems to agree perfectly with this maxim, because by that means the flank so raised covers as much as possible the face of the opposite bastion; but notwithstanding this apparent advantage the flank becomes too small and is too much exposed to the enemy’s batteries. Thisengineer acquired great reputation during the several sieges which he assisted in conducting under Louis XIII. His system has been improved upon byAlain Marrison Mallet, and his construction in fortification is to this day esteemed the most perfect. It differs very little from Marshal Vauban’s first system. Count Pagan has pointed out the method of building casemates in a manner peculiar to himself.
Marshal Vauban has judiciously steered between these different methods. He has drawn his flank in such a manner, that it does not stand too much exposed, nor does its collateral line of defence extend too far from the direct line of defence. He has effected this by lengthening out his flank and giving it a circular form.
It cannot be disputed but that large and extensive flanks and demi-gorges are superior to narrow and confined ones. The more capacious the flank is, the better calculated will it prove for the disposition of a formidable train of artillery. From this conviction many writers in their proposed systems of fortification, have added a second flank, in order to augment the line of defence; but they did not foresee, that this second flank is not only incapable of covering the face of the opposed bastion, except in a very oblique and insecure direction, but that the right flank, or the flank of the bastion, is thereby more exposed to the enemy’s batteries, which, it must be acknowleged, is a great fault.
The prevailing system of the present day is to make the flanks of the bastion as wide as possible, without having recourse to a second flank, unless it be absolutely necessary. Those gorges are likewise best which are most capacious, because they afford space and ground in the bastion for the construction of intrenchments within, should the enemy have effected a practicable breach.
All parts of a fortification which stand exposed to the immediate attacks of a besieging enemy, must be strong enough to bear the boldest attempts, and the most vigorous impressions. This is a self-evident maxim, because it must be manifest to the most common understanding, that works are erected round a place for the specific purpose of preventing an enemy from getting possession of it. It consequently follows, that flanked angles are extremely defective when they are too acute, since their points may be easily flanked and destroyed by the besieger’s cannon.
The Dutch construct at sixty degrees; but according to Vauban’s method, no work should be under seventy-five degrees, unless circumstances and situation should particularly require it.
A place to be in a state of defence, should be equally strong in all its relative directions; for the enemy would of course make the weak part his object of attack, and finally succeed in getting possession of the town. The body of the place must have a command towards the country, and no quarter in the outward vicinity of it must overlook, or command either the place itself, or its outworks. Those works which are nearest to the centre of the place, must have a greater elevation than the more distant ones.
The first regular system of fortification which appeared and was adopted in France, owed its origin to Errard of Bois-le-Duc, whom we have just mentioned. His method, however, has been uniformly rejected by able engineers; and if we may give credit to the report of Ozanan, Errard himself never carried his own system into practice.
Next to Errard of Bois-le-Duc, came the Chevalier Antoine de Ville, who was engineer under Louis XIII. and published an excellent treatise upon fortification. His method is stiled by most authors, theFrench method. Others call it theCompound System, orSysteme à trait Composé, because it united the Italian and Spanish methods. He was, indeed, by no means an advocate for new systems; for he generally observed, that any new method, or invention was extremely easy, so long as it was confined to the mere alteration of something in the measure, or in the disposition of those parts of fortification which have been discussed by other authors.
The Count de Pagan followed after, and had the good fortune to propose a system which entirely superseded the other two. We have alreadymentionedthe principal feature, in hismethod.
Marshal Vauban, whose reputation rose upon the manifest superiority which his skill gave him over all others that had written upon fortification, likewise proposed three methods, with considerable improvements:viz.Thegreat, themean, and thelittle.
The great method, according to Vauban, contains on its exterior side from 200 to 230, or 240 toises. This extent is not uniformly the same throughout all the sides of a place, but is confined to that side which lies along the banks of a river, where he uniformly erects considerable outworks.
Vauban made use of his second method in fortifying Béfort and Landau. On account of the bad local situation of Béfort, and the impossibility of fortifying it with common bastions that would not be exposed to an enfilade in almost every direction, in spite of the traverses orrechuteswhich might be made: he invented arched bastions that were bomb proof, which he calledtours bastionnées, ortowers with bastions. These arched bastions are covered by counter-guards, the height of whose parapet almost equals the elevation of the towers themselves. Although strictly speaking, both these places are irregularly fortified, nevertheless a methodof regular defence may be established from the construction of their works.
Vauban’s third system grows out of the second, and for that reason it is calledordre renforcé, thereinforced order or method. It was adopted in the fortifications of New Brisac. Vauban left nothing untried to bring this system to perfection, and he had the ingenuity to execute his plan at a less expence, than it would otherwise have been effected, by means of half revetements which he threw up in the outward works called the dehors.
This system, however, (ingenious and unrivalled as it certainly is,) has not escaped the censure of some writers. It must nevertheless be acknowleged, that their remarks are either founded in envy, or that they proceed from ignorance.
There are other systems of fortification which have been proposed by the writers of other countries besides France. We shall give a brief detail of them, and leave the inquisitive to go more at length into the nature of their methods, by referring them to the different treatises.
The Italians have furnished several authors who have written variously on the subject of fortification. The method proposed by Sardis has been generally esteemed the best.
The Spaniards in their methods of fortifying, never adopt that which adds a second flank. The obtuse flanked angle is not looked upon by their best engineers as a defective system in fortification.
Both the Italians and the Spaniards speak frequently of theordre renforcé, which was originally invented to lessen the number of bastions in a great town or fortified place, and to render consequently the line of defence equal to the range of musquetry.
The Chevalier St. Julien, a very able engineer, has published a method, by which, he asserts, that works may be constructed not only at a less expence than others require, but in a manner that must render his defence or attack more formidable. He has likewise invented a new method for the defence of small places, which is preferable to the first, although it is not without faults. According to his system, the reach of the musquet is taken from the centre of the curtain. To this end he directs, that a covert lodgment, 7 feet high, and 10 toises wide, be constructed from that spot to the gorge of the half moon or ravelin. Cannon is disposed along the faces, and a gallery is erected for the musquetry, which likewise serves as a passage to the ravelin.
Francis Marchi, a gentleman of Bologna, in his folio edition, has furnished us with upwards of 160 different methods of constructing fortifications.
The Dutch uniformly pursue the system published by Marollois.
Bombelle has likewise established three sorts of fortification, the great royal,grand royal; the mean; and the little royal,petit royal. His method agrees with the sound maxims of good fortification much more than any of the preceding ones.
Blondel has published a system of fortification, which he divides into two principal heads; thegreat, whose exterior side contains 200 toises; and thelittle, where the side does not exceed 170 toises. His reason is, because he objects to the line of defence having more than 140 toises, which is the furthest reach of musquetry, or less than 120 toises, to prevent an unnecessary increase of bastions. The principles of Blondel’s system resemble, in a great degree, those upon which Pagan’s is founded, and chiefly consist in methods of fortifying inward posts. The invention has certainly great merit, but its adoption must prove expensive in all its practical branches. It must, moreover, be manifest, that the four long batteries which are supported by flanks of his construction, must serve as so many scaling ladders, or steps to the besiegers, the instant they have effected a breach by cannon shot, or shells.
In 1689, a work was published, entitled:
Nouvelle maniere de fortifier les places, tirée de methodes du Chevalier de Ville, du Comte de Pagan, et de M. de Vauban; avec des remarques sur l’ordre renforcé, sur les desseins du Capitaine Marchy, et sur ceux de M. Blondel.This work is full of strong reasoning, from the result of which the author has formed a new method, containing indeed, nothing original, but giving references to what has already appeared, and disposing the different parts in so judicious a manner, as to shew how a place may be rendered stronger, and be subject at the same time to a less expence. This writer divides fortification into three parts, the great, the mean, and the little.
There is a second and a third method proposed anonymously, and containing mere simple designs. That method in which a modern author gives it the preference over the system of New Brisac, contains little useful information, and contributes less to the real art of fortifying places.
Donato Rosetti, a Canon belonging to Livournia, professor of mathematics in the academy at Piedmont, and mathematician to the Duke of Savoy, has written upon a method of constructing works in what he callsfortification à rebours, or fortification in reverse; so called not only because the re-entering angle of the counterscarp is opposite to the flanked angle; but because, in his idea, it will be necessary to attack it from the reverse side of other works. His system is very simple, and does not require a sacrifice of much money, or stand in need of many men to defend the works: although hecan, on his side, pour as much fire upon the enemy, as could be furnished by more complicated methods.
Antonio de Herbart, major of artillery, in the Duke of Wurtemberg’s service, in 1735, published a treatise on fortifications with square angles, which he callsangular polygons.
Monsieur de Montalembert has lately endeavored to bring arches, which are so much condemned by the Chevalier de Ville, into repute. He treats the subject in a manner, and upon principles so similar to those proposed by Antonio de Herbart, that it is almost impossible to separate the two systems. M. de Montalembert asserts, that the science of fortification, (as it is established and taught at present) can only be valued by the public on account of its illusion. He looks upon the use of bastions, as the effect of prejudice; he rejects them wholly, and substitutes in their room, a front ofangular tenailles, polygons with small wings, and angular polygons. The engineers of the present day assert with confidence, that the chief security to be derived in works that are supported by bastions, must depend upon cross and reverse firing directed against the enemy’s lodgments on the glacis. Large half-moons are made, not only for the purpose of covering the curtains and the flanks of bastions, but principally to obtain a reverse firing, which effectually prevents the enemy from maintaining his ground on the glacis of a bastion, before he has taken the two collateral half-moons.
M. Menno, Baron of Coehorn, who was general of artillery in the Dutch service, lieutenant-general of infantry, director-general of all the fortified places belonging to the united provinces, and governor of Flanders and all the fortresses that lay along the Scheldt, has been justly esteemed for his extensive knowlege in the art of fortifying places. He was cotemporary with Vauban. This intelligent and sagacious officer being thoroughly convinced, that, however expensively the rampart of a town may be constructed, it could not long sustain the shock of heavy ordnance, invented three different systems, by which he throws so many obstacles in the way of a besieging enemy, that although the place be not in reality rendered impregnable, it is nevertheless so far secured as to make its conquest a business of considerable hazard and expence. We must however acknowlege, that the three methods which have been pointed out by this Dutch general, can only suit places and grounds that are nearly on a level with the surface of the water; that is to say of 3, 4, or 5 feet; which circumstance plainly indicates, that his attention has been chiefly directed to the soil and ground of Holland; so that his instructions are peculiarly applicable to low and aquatic situations. There is much skill discovered in his manner of treating the subject, and considerable ingenuity in the treatise he has published, which certainly contains several improvements that are exclusively his own. It would be impossible to force a passage, or to penetrate into any of his works, without being exposed on all sides, to the fire of the besieged, who are under cover, and from whose discharge of ordnance and musquetry, it is scarcely possible for an assailing enemy to secure himself.
Scheiter, a German writer, describes two kinds of fortifications, thegreator thesuperior, and thesmallor theinferior species. It has been erroneously and unjustly stated, that the celebrated Vauban only copied after Scheiter, at New Brisac.
Every man of the least knowlege or penetration must see, that the whole system of that illustrious engineer differs essentially from the author we have quoted.
The defects which are manifest in all these different systems shew the superiority which exists, to this day, in all the fortifications that have been constructed by Vauban.
An anonymous writer in the Sardinian service, proposes two new methods of fortification in a work entituledScience de la Guerre, which was published at Turin, in 1744. After having discussed, at considerable length, the art of fortification in general, its utility, the different sciences which must be acquired towards obtaining any degree of perfection in that art, the various systems in it, regular and irregular, and the construction of palisades, gates, mines, casemates, magazines, &c. &c. he concludes with this extraordinary sentence: “It is not my intention to propose any alteration in the general system, but merely to suggest, that the style be rendered more intelligible.” It must be noticed, that this Italian writer in his preface, frankly confesses his deficiency in the French language. We shall however pass over what he says relative to the approbation which his proposed systems, or rather his explanation of methods already known has met with from scientific men, and give his own observations concerning the improvements that might be made. His wordsare—
“The first method which I propose, consists of a new figure and position that should be given to exterior works in fortification. Having constructed the body of the place after Vauban’s manner, my next object is to erect counter guards with bastions at the head, and flanks upon the wings. I have been induced to adopt this species of work, in order to remedy the inconveniences and the dangers which invariably attend works erected at the foot of the glacis. These works contribute very little to the security of the place, and can only be defended bycannon, which eventually do more harm to the garrison than to the besieging enemy, since they serve as an epaulement to the battery, which the latter will naturally erect the instant he obtains footing in that quarter. This was proved during the siege of Turin, where in a very short space of time the French carried the bonnets and fleches, and made use of them for the purpose of bringing up their artillery.
By means of the small bastions which I have proposed, and which must be pushed forward into the country, the enemy’s approaches are necessarily checked, the saliant angle of the counter-guard is covered, the ditch is completely flanked, and the garrison are impressed with confidence, because the artillery and the troops can always be called in, in cases of exigency. They moreover equal the enemy in the fire which they can furnish, and the whole body of the place is covered by them.
I construct the bastions and flanks out of the sides of the counter-guard, which are detached by means of a ditch 4 toises wide. This ditch is covered above by vaults made of brick or timber, and by boards well supported underneath by strong stakes, the whole being strengthened and rendered bomb-proof with earth 3 or 4 feet thick. This earth keeps the upper plan of the bastion compact, and is sufficient to form a parapet to the counter-guard when the bastion is destroyed. If the vaults should be blown up by mines, and the besiegers set fire to the beams that supported them, a fresh work will present itself, together with a ditch which they had not foreseen or expected, and which they must cross before any further impression can be made.
This sort of subterraneous fortification is extremely advantageous, and may be converted to various purposes. It serves for casemates and galleries to the mines, which I would construct along the whole extent of the faces belonging to these bastions; a communication with them is kept up by means of the galleries attached to the counter-guard. These galleries must be blocked up the instant the bastion is demolished. The flanks of the side will be built after the same method, with a ditch as wide as the one dug in front of the bastion, and which, according to circumstances, may be uncovered, like that already described. The flanks will be of a round figure, in order to avoid the projection of any angles towards the body of the place, which would be the case, should the work be carried; for the enemy availing himself of the earth in front of the walls, and throwing it up, would derive considerable advantage from these angles.
The principal advantage to be obtained from my system arises out of the double defence which it affords to the saliant angles of the bastions, by covering a part of thedemi-lunes mitrées, or mitred half-moons (which are their chief protection,) and by these means concealing the body of the place from any outward command, or eminence. This cover or defence cannot, in fact, be taken, before the enemy has got complete possession of the outworks.
I have spoken of these sorts of fortification in the chapter that treats of field works, which, in my humble opinion, are more useful, more solid, less expensive, and more easily built than a variety of others that have been adopted to this day.
The demi-lunes or half-moons which are nearly mitred or crossed, and which I dispose between the counter-guards, have been constructed in that manner for the purpose of stretching as far as possible, beyond the body of the place towards the country. One essential advantage attends this method, which is, that the work being more spacious, it is better calculated to hold a greater quantity of artillery, and a large garrison; that it becomes double by means of the ditch, which separates it from the advanced work, which it covered as described above, and which is joined to the interior revetement by plain walls, separating a whole half-moon from it; in which space a small fort with loop-holes may be constructed to enable the garrison to dispute every inch of ground as the enemy advances. Under the main body of the place, I build a subterraneous chamber, to serve as occasion may require, either for a powder magazine, or for mines.
Between the half-moons and counter-guards, I construct another kind of ravelins, which are open towards the body of the place, cover the curtains of the counter-guards, and supply a double fire against the enemy and the covert way. These ravelins are not raised so high as the other works, in order to keep them under their fire; and I preserve a communication by means of palisaded caponnieres. I leave them empty within, that the besiegers may have as little ground as possible; they are moreover sufficiently thick and solid to withstand the discharge of ordnance, which can only batter in breach from the counterscarp, which acquires double strength, because by means of these works, it is enfiladed, and secured against the enemy’s attack or attempt to make a lodgment.
If the plan, which I had the honor of laying before the king of Sardinia, be carefully examined, it must be apparent to every military man, that the works I therein describe, are not only more useful, but capable of being constructed at a less expence, than those which are generally practised to this day. It will be clearly seen, that I have done nothing more than add some additional proportions of the flanks and bastions to the counter-guards, which are usually erected;and that I have augmented their double face, by joining it to the half-moons of the curtain. The object of this addition, is to throw obstacles in the enemy’s way, should he attempt to make close approaches, to cover the body of the place, to render the siege difficult, to increase the besieger’s expence, and to give confidence to the troops of the garrison, who are thereby no longer exposed, as they must be in all outworks erected upon the foot of the glacis.
It is not, however, my design to throw works of this kind into utter disrepute. There are situations and local circumstances, which not only make their adoption useful, but render it absolutely necessary. I cannot pretend to describe the specific nature of such exigencies, as they grow out of existing cases, which an able general and an engineer will know how to discriminate by examining the ground.
The ditch belonging to the body of the place, be its soil what it may, must be very broad, as the chief security to be derived from it, depends entirely upon its width. The enemy cannot easily fill it up, and he must suffer a considerable loss of men, should he attempt to cross it; being exposed to the discharge of artillery from the flanks, which artillery cannot be dismounted from any quarter or lodgment, before the counter-guards are taken. The storming of the place must depend entirely upon the previous conquest of the side ravelins, and of the centre half moons; for unless the enemy has first effected this, he will not be able to cross the ditch, or make any lodgment, since at every approach he must be annoyed from the flanks, and battered in front; he must, in fact, attack and get the better of five works at once. The execution of any part of so important a task, must be the more dangerous, because in proportion, as he overcomes one line of defence, another presents itself which is equally formidable, and the rest increase in difficulty and hazard.
When I submitted this new method to the consideration of able and intelligent men, only one opponent started to controvert the property of its general adoption. This was a celebrated Dutch engineer, who asserted that it could not be of any essential service, except in hexagons, or figures that had many sides; he further argued, that the method was more faulty in small works, because the angles became more acute, and that no use could be made of them in regular fortification.
I had the good fortune to satisfy this gentleman, and to convince him, that his objections were not well founded. I stated to him, that by increasing the width of the ditch at the angle of the flanks of the bastion, I reduced that angle to any size I judged necessary; I maintained, that by so doing I did not weaken the place; but that on the contrary by cancelling the parallelogram of the counter-guards, I rendered more oblique any battery which the enemy might erect in front of the bastion, whilst the rampart belonging to it fell under a cross fire from the mitred half-moon.
With respect to its uselessness in irregular fortification, after having discussed the subject at some length, I got him to agree with me, that every detached piece of fortification might be constructed any where (and with greater advantage to the ultimate defence of a place) sooner than in plain counter-guards, horn or crownworks, tenailles and such like fortifications, because by means of the retreat which was secured under a second line of retrenchment, by means of the regular resistance it afforded, without having one dead angle attached, and by means of the little ground it left for the enemy to lodge on, the main body of the place was more effectually protected, and the approaches of the enemy were considerably checked.
With regard to the construction proposed in this new method, I take all the measurements, and I mark all the essential points upon capital lines; that is to say, I prolong the lines of the saliant angles of the bastion, and those of the centre of the curtain; after which I determine the width of the ditch at 23 or 24 toises, in order to make the parallels of the faces of the different bastions for the counterscarp of the counter-guards and of the great half-moon, and finally the thickness of the works, to agree with the ditches in front.
With regard to the ravelins which are made between the mitred half-moons and the counter-guards, I place the saliant angle in the centre of the scite, and I construct faces to them in such a manner, that they are under a straight line of defence from the half-moons and counter-guards. I erect the counterscarp and glacis in the usual manner, only with this difference that I wish to have a ditch of moderate breadth and depth between the covert-way and the glacis: say, two toises broad upon two deep.
In order to clear the ditch of occasional rubbish that may fall in, or of pieces that may drop from the demolished parts of a fortification during a siege, square excavations or wells must occasionally be made along the flanks and faces of the different works; by which means the ditch is always kept clean, and you may at any time repair the fortifications, whilst on the other hand, the enemy, should he attempt to storm the place, must have recourse to fascines, as he could derive no advantage from the materials that would otherwise be found under the walls.”
This ingenious writer has described every part of the method proposed in a clear and perspicuous manner. His plan is particularly valuable, on account of the exact measurements it contains, wherebythe most common understanding may become acquainted with the construction. He appears singularly anxious to have it practically proved, that works can be erected according to this method at a less expence than by any other, and that there is no comparison between the advantages it affords in point of real utility. In chap. 16, p. 61, the following account is given of his second system, which he calls theGreat System.
“After I had thoroughly digested my plan, relative to the best method of covering a town or fortified place by outworks, it naturally occurred, that I had not provided the necessary means of keeping the troops under shelter, of securing a retreat to the artillery, which is always seized whenever a work is taken by assault, nor of furnishing a heavier discharge of ordnance and musquetry than the enemy could pour in. These important objects put my invention to work, and I directed all the faculties of my mind towards discovering a kind of fortification which might not only cover the body of the place, and by a new disposition of its relative parts communicate equally with every quarter, without there being any necessity to carry the heavy ordnance into the ditch; but likewise oblige the besieging enemy to increase his means of attack, and make extraordinary efforts. I necessarily saw, that the saliant angles of the bastions should be well covered, and that the strongest ought to be raised before the curtain belonging to the body of the place, in order to force the assailants to make their attack on a quarter from whence the concentrated fire of several works, presenting a wide front of artillery, would issue with considerable effect.
After having for several years, directed the whole of my attention to this specific object, and tried the result of my reflections upon paper by a variety of designs; I had the good fortune to discover a method, whose plan exhibits to the eye several pieces that are joined together by their different walls, and in front of which there are ditches covered in with beams and strong oak boards, and made bombproof by means of a sufficient quantity of earth that is spread upon the whole. So that it appears evident to me, that there is only one species of fortification, which affords the means of concentrating your line of defence from every quarter, and of lining the parapets with heavy ordnance. By means of this construction, the lines and glacis will be secured against any immediate approaches of the enemy, during which seasonable interruption, the artillery may without risk, be withdrawn and lodged in the interior work; a convenience which cannot be obtained in detached pieces, on account of the difficulty which always attends the first erection, or ultimate demolition of them.
By taking away the beams, or by destroying them at once, and by pulling down the walls which compose the flanks, you suddenly open a new work upon the enemy; which work has the advantage of being considerably larger than the one he has just attacked and taken, and against which he must raise fresh batteries, and prepare the means of crossing a ditch, he had not foreseen, and which he cannot easily pass. This work either communicates with a tenaille that commands it, or is connected with a horned work, flanked by two others of similar construction. The tenaille is open in the centre (being divided into two parts by a ditch) in order to leave as little room as possible for the enemy to lodge on, and to multiply the enfilading points of the place.
Between these large works, demi-lunes or half-moons, of three orders, are constructed in the shape of bastions. These have orillons and ditches between the two, which flank the side-works, and are always protected by an enfilade, that the enemy never can lodge without being exposed to a cross and rear fire. In order to cover the whole body of the place, I construct other intermediate demi-lunes, which are equal in elevation to the first works. These contribute greatly towards preventing the enemy’s approaches; for they not only enfilade the covert-way, but they likewise double the defences in such a manner, that the enemy, as has already been observed, cannot attack one place without experiencing a necessity to attack four others at the same time: to which may be added this disheartening circumstance, that as fast as he advances, so fast a retreat is made behind some new work, and he is, of course, obliged to recommence his attack.
The regular communication between the several works must be kept up by means of sleeping bridges, which are well supported underneath by strong beams or stakes. Those which form a part of the rampart must be covered with four feet of earth, well pressed together. The walls by which the works are connected, must be so built as to be easily demolished, and they must only serve to cover the subterraneous fortifications. These walls are never within the reach of the enemy’s cannon, and when they are pulled down, their ruins are thrown into wells, or excavations, which have been previously dug at the foot of the main wall, to prevent the ditch from being filled with them: subterraneous embrasures are opened from within to enfilade the ditch, and to obstruct the passage.
When by dint of perseverance, and after having expended considerable sums of money, lost many lives and consumed much time the enemy has at last obtained possession of these works, he discovers, that his sacrifices have only led him to an unexpected body of the place which he cannot injure. This new constructionhe finds flanked on both sides by two double bastions, and a broad curtain lined with a triple front of artillery, having a very wide ditch, traversed by tenailles, batteries from casemates, and defended by flanks with the two cavaliers belonging to the bastions, which keep up an incessant fire upon the artillery that is planted in the carried outworks, and render it almost impossible for him to establish a lodgment.”
“I need not pretend,” continues the same author, “to have discovered by this new method, any certain means of rendering a place impregnable; such an idea would be chimerical and absurd.
Let a town be ever so well fortified, that town, if properly invested and resolutely attacked, must eventually fall, unless it be seasonably succoured from without. My chief object is to correct the errors into which former writers seem to have fallen, and by the methods I have proposed, to harrass a besieging army, not only by increasing its expence, but by occasioning a considerable loss of men; I thereby prolong the siege, and gain time for the garrison, so that succours may arrive, or such conditions be entered into as will secure the country, which the place attacked is destined to cover.
Counter-guards, ravelins, and demi-lunes are, in fact, a species of fortification by which they flank one another obliquely, and which only tend to embarrass the troops of the garrison, whenever it is judged expedient to manœuvre under the fire of artillery; a circumstance that invariably causes confusion; whereas the works which I have proposed are capacious enough to admit of every movement and evolution without inconvenience.
Horned and crowned works are extremely expensive in their construction, and of little use when completed; their lines of defence, their faces and their flanks are so short and limited, that a besieging enemy can with great ease attack, and carry them by means of an equal front and range of fire: and when he has so far succeeded, he derives considerable advantage from having opened a wide space of ground on which he can erect angles to annoy and batter the place. Whereas in the works of my proposed method, the foundations are broader, the defences are more direct and within musquet shot, and when the garrison retreats towards the body of the place, the ground which it abandons is scarcely sufficient for the erection of a small battery; it is moreover exposed to all the retrenched and flanking points, so that the enemy would be instantly dislodged.
Tenailles andqueues d’hirondellecontain dead angles which may always be taken advantage of by the besieging enemy. This does not exist in the works I propose. For at every approach, not only fresh expences must be incurred by the assailant, but he will remain exposed to several fires at once, without being able to cover himself from the reverse and cross ones.
Double ditches afford the means of creating perpetual uneasiness in the enemy, by uncovering fresh works as he advances. So that the siege is protracted, his expences are increased, and his loss of men, ammunition, stores, and artillery is proportionably multiplied.
In the examination which was made of thereliefproposed by me; some persons well acquainted with the particular subject, objected to its adoption on account of the expence. I made an accurate calculation of the amount, and I found that it cost a sixth more than the usual fortification. This does not assuredly form sufficient ground to outbalance the many advantages which can be derived from the construction. Besides, there is no occasion of fortifying all the parts of a town in this manner, since it would be advisable to strengthen the weak points only.”
The construction which is proposed in this new method, is simple, and easily understood. The principal objects to be attended to are these; that there be mines under all the works, and that a regular communication be kept up with the chambers by means of subterraneous galleries, which must be resorted to in proportion as the enemy approaches.
The Piedmontese engineer, from whom we have made these extracts, has added to Vauban’s and Coehorn’s systems. We leave the subject to the consideration of those professional men who have made the art of fortification their peculiar study; they must determine whether the theory of the proposed method be susceptible of practice, and if so, whether it can be rendered so generally useful, as the author seems to promise it would.
On a general view of the subject it must, however, be acknowleged, that a situation is not always found which will admit of the improvements and additions that might otherwise be made. There are some old places in which the figure of the fortifications erected for their defence, is so strange and whimsical, that the least correction of its errors, must be attended with an enormous expence.
A town may be irregularly fortified, and owe that irregularity either to the figure of the works only, by the angles not being equally distant from the centre, although every one may admit of a good bastion, and the lines be tolerably extensive; or by the figure and the angles differing, from some being too acute, and others being rentrant; or by the inequality of the figure and its sides; some being too long and others too short; or finally by a disparity all together in the figure, in its sides and angles.
If the three first kinds of irregularityare judiciously corrected, the correction of the fourth follows of course, as it is only the natural consequence of the others. Those irregularities may be occasioned by a neighboring river, by the entrance into a creek or harbor, or by steep rocks beyond which it is impossible to carry the works.
It is a sound and general maxim in the art of fortifying, to reduce the irregular proportions of its lines, &c. of defence to as much regularity as the ground and situation will permit. For by so doing, their strength becomes equally great throughout. If you should not be able to surmount the natural obstacle which may be thrown in your way, you must never deviate from the general rules that are laid down in regular fortification. These are, that all the parts be well flanked, that the angles of the bastions do not fall under sixty degrees, that the line of defence be within musquet shot, or that outworks be established to bring it within that range; and finally, that the means of resistance be distributed in as many equal proportions as the irregularity of the works will suffer.
You must, however, be careful to avoid an error into which many have fallen. You must not weaken the collective means of defence, in order to strengthen any particular vulnerable quarter; for by so doing you are sacrificing a great line of defence, to the security of a small part which might be strengthened by outworks.
The author of Oeuvres Militaires, in his 3d volume, page 45, has given observations and maxims relative to irregular fortification.
Baron d’Espagnac, in consequence of the remarks which are made by Marshal Saxe, in hisReveries, has in his supplement to that work amply discussed the subject of fortification, and described the different means of attack and defence. We refer the inquisitive officer to those works. Before we conclude these interesting remarks upon an art, which is certainly equal to any invention that has employed the skill and ingenuity of man, we must observe that in all periods, productions on that head have been as numerous as the subject has hitherto proved inexhaustible. It must, however, be acknowleged with some regret, that the tendency of the greater part, if not of all, seems to be an indiscriminate and bold attack upon the works of the immortal Vauban. These writers censure the methods of that great engineer by proposing something of their own, which only differs in appearance, and which they think proper to call asuperior system. Assertions, and promises to afford new lights upon the science of fortification, have always, in fact, been profusely given by authors of this description. Their labors, however, are only so far to be regarded and esteemed, in as much as their different systems tend to point out the necessary calculations which are required to shew the expence attending their construction, and to prove the effects they might produce. The memoirs upon perpendicular fortification, written by M. Montalembert engineer, will throw considerable light upon these observations.
With respect to the knowlege of fortification, it must be manifest to every thinking man, that from a chief magistrate, or head of a country, down to the lowest infantry officer, the acquirement of it is more or less indispensibly necessary.
A chief magistrate of a country, should be well versed in the science of fortification, in order to examine the plans that are laid before him, and to determine upon the execution of proposed projects.
A secretary of war should know it, in order to explain the nature of the plans when questioned by a superior power, to calculate the expences which will attend the construction of works, and to distinguish good ones from those which might be useless and expensive.
Every commandant of a town or fortified place, should be well acquainted with the subject, because it may fall to his peculiar share to construct works in cases of emergency, or to add to those already erected for the defence of the place entrusted to his care. He likewise ought, at all times, to be able to ascertain how far such a place is capable of holding out.
Every director of fortification should be master of it, in order to discriminate between what is proper, or what is defective, and make his report accordingly.
Every infantry officer, in a word, should be conversant in field fortification at least, if not acquainted with the general system. For without some knowlege of its branches, how will he, in cases of emergency, be capable of throwing up a temporary redoubt, of fortifying a spot of ground which he is ordered to maintain, or of securing a common outpost?
FieldFortifications,fortifications de campagne,Fr.consist in the art of fortifying, constructing, attacking, and defending all sorts of temporary field works during a campaign.
Although an engineer may be perfectly master of the different methods by which a town can be strengthened and secured by permanent works, he should not remain satisfied with that acquisition, but carefully direct his attention to the distribution of ground, for field fortification. He should be able to ascertain, with geometrical precision, all the relative divisions and corresponding points of any situation in which it might be judged expedient to construct that species of fortification which consists in intrenched lines, fortins, or small forts, and in redoubts of various denominations. Theshape or figure of these works is exactly similar to those of the permanent kind. Ditches, ramparts, and parapets must be dug and thrown up, to secure the former, in the same manner as they are practised for the protection of the latter. They only differ in their measurement and proportions. Intrenched lines are made for the purpose of covering a camp from any sudden insult of the enemy, which should always, on this account, be pitched in the most advantageous manner; contiguous to and facing that quarter where it is probable the attack will be made, a ditch must be dug, having three toises at least in width and two in depth. This must be defended by a parapeten redans, or be occasionally flanked with small bastions, two toises thick, consisting of solid good earth well pressed together, covered and supported with fascines; having likewise banquettes behind them sufficiently high to conceal the soldiers’ tents. If water could be conveyed, or drawn into the ditch from any adjacent rivulet, or river, the security would be greater. When the lines of intrenchment are thrown up with an intention to maintain the ground any length of time, a covert-way must be made, which should be regularly fenced with palisades.
There is another species of field fortifications, which is resorted to in order to keep up a communication between two places; in which case great care must be taken to prevent the lines from being enfiladed in any quarter; and if they should be exposed in that manner, no time ought to be lost in strengthening the weak points by constructing redoubts, or small forts. The defence of these redoubts and forts must be entrusted to small arms and musquetry, but not to cannon, as the range of the latter is always too extensive to prevent an enemy’s close approaches to the lines of communication from their field works, or forts. Necessary drains must be made to let out the water that collects, as it would otherwise destroy the works, drown the sentries, and cut off all communication with the main body.
When a position is taken upon a steep rock, or eminence extremely difficult of access, the lines which surround it do not absolutely require ditches for their safety, as the parapet and banquette may probably be sufficient; but if any vulnerable or weak part be observed, every effort should be used to get at a spring, and to fill up an excavation in front of it, to prevent surprises. An able engineer will be particularly careful in drawing his plan of communication, to ascertain the exact points whereby they may be protected by an enfilade from one fort to another; so that if the enemy should make a lodgment any where, he will not be able to maintain his position on account of his being flanked by other works.
Field works, or small forts are generally constructed in places the preservation of which is judged to be indispensibly necessary. Such, for instance, are necks of land that stretch into a marsh, and are surrounded by it; the passage of a road,têtes de ponts, or heads of bridges, and other objects of similar importance in offensive, or defensive operations. On these occasions the shape and size of the construction must depend upon the nature of the ground, the importance of the undertaking, and on the number of men by which the works are to be garrisoned.
Many forts in field fortification are built in triangular forms; some are square, some starred, oren étoile, some as redoubts, in the shape of demi-lunes, others in crown, or horn-work, and others again in the figures of tenailles orqueues d’hirondelle.
When the object of defence is a windmill, a castle, or a small dwelling-house, the first step to be taken, is to select a spot of ground upon which you are to build the field work, so as to check and prevent the enemy’s approaches. In order to do this effectually, the shape and adjacent parts of the building must be closely attended to, and the work be thrown up without exposing it to a rear attack; but if the place to be defended stand alone, and be not supported by any ditch or eminence on its flanks, or in its rear, you must then fortify it all round. The earth which is dug out of the ditch will serve to raise the rampart, or parapet. Saliant angles, distributed at equal distances, in the shape of bastions, must be erected with good flanks to protect and cover the intrenchment. If, on account of the ground, the work should not be much raised, the parapet must be raised, in order to prevent the enemy from attempting an easy assault.
An engineer from Piedmont, who has proposed some new methods in field fortification, is decidedly against stone and masonry, in the construction of parapets and field works. His reason is self-evident; for as he justly observes, the scattered pieces which must naturally be thrown about in all directions by the demolishing of the walls in the discharge of heavy cannon, would do more mischief than the cannon itself.
It is frequently found necessary to fortify a bridge; the means adopted for this purpose must depend entirely upon the size and current of the river. If the stream should be broad and navigable, and so far from the fortress, that it cannot be defended by the ordinance of the town or fortified place, in that case a large retrenchment, resembling a place of arms, must be constructed, with strong bastions to support and cover it, curtains and half-moons, a broad and deep ditch, and covert-way that must be well secured by palisades. This retrenchment, or place of arms, must be made sufficiently capacious to hold a garrison that wouldbe capable of opposing the attack of a large detachment from the main army of an enemy. A half-moon must be constructed within the lines, with a ditch in front, to serve as a work behind which the garrison might retreat with its artillery, disputing every inch of ground, and by that means affording sufficient time to cut down the bridge.
If the river should be narrow, yet wide enough to prevent any sudden irruption into the country beyond it, the bridges that are across must be fortified by works made of earth, which are to be covered by ditches dug in front. Half-moons, tenailles, crown and horn-works, and similar constructions, provided they be well fenced with palisades, will answer all the purposes required in such cases. The engineer, by the first glance of his eye, will be able to ascertain the situation of the country, and to fit his plans accordingly. Small lodgments, or wooden recesses, must be made as guard-houses, in which detached parties of men should be stationed to meet the first attacks of the enemy, and to keep him in check while the whole army passes over the river, or is drawn up in order of battle to dispute the passage. These intrenchments must invariably be well furnished with light artillery, for the purpose of annoying the approaching enemy. But the disposition and arrangement of these pieces must always be such as to admit of their being instantly removed, when the intrenchments are carried, under the cover of heavier ordnance which is kept playing upon the enemy from the opposite side of the river.
Practical Maxims in building Field Works.1st. The spot on which works are to be constructed should determine their figure; nor should any attention be paid to preserve a regular form which does not occupy the ground to advantage.
2d. Every line must be so disposed, that the slope of hills all around even to the very bottom, be open to the small arms of the garrison; and every part should be discoverable to the distance of at least 500 paces.
3d. Works thrown up for the defence of a defile, should always be within musquet shot of it, which must not be more than 200 yards.
4th. The best defence in works that are flanked, or where one side is defended by the fire of another, is that formed by right angles.
5th. A saliant angle should never be less than 60, and a re-entering angle than 90 degrees; nor greater than 120 degrees.
6th. The entrance to the work should always be made in the part least exposed to attack, and if possible in a re-entering angle.
7th. Endeavor to present, if possible, a larger front to the enemy than he can occupy in making the attack.
8th. Avoid all ground commanded by an eminence, either in front, flank, or rear.