Part 43

_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 intrenchment_ are 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.

_Redans_ are 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 redans_ are 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._ See _Bridge-heads_.

_Trous-de-loup_ are 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 works are 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.

_Subterraneous_ FORTIFICATION.

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’s _Elemens 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.

+-----------------------------------+---------------+---------------+ | The great FORTIFICATION. | The mean. | The little. | +-------------------+-------+-------+-------+-------+-------+-------+ | | for |for all| for |for all| for |for all| | |squares| other |squares| other |squares| other | | | | poly- | | poly- | | poly- | | | | gons | | gons | | gons | +-------------------+-------+-------+-------+-------+-------+-------+ |Exterior side | 200 | 200 | 180 | 180 | 160 | 160 | +-------------------+-------+-------+-------+-------+-------+-------+ |The perpendicular | ?7 | 30 | 24 | 30 | 21 | 3? | +-------------------+-------+-------+-------+-------+-------+-------+ |The face | 60 | 60 | 55 | 55 | 45 | 50 | +-------------------+-------+-------+-------+-------+-------+-------+ |The flank | 22 | 24 2| 19 1| 24 | 18 3| 23 2| +-------------------+-------+-------+-------+-------+-------+-------+ |The curtain | 73 2| 70 5| 63 4| 60 4| 63 5| 50 4| +-------------------+-------+-------+-------+-------+-------+-------+ |The line of defence| 141 4| 141 2| 126 1| 126 5| 115 5| 112 3| +-------------------+-------+-------+-------+-------+-------+-------+

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. || +-----------------------+---+---+------+---+---+---++ |Side of Polygon | 80| 90|100 |110|120|130|| +-----------------------+---+---+------+---+---+---++ |Length of perpendicular| 10| 11| 12¹⁄₂| 14| 15| 16|| +-----------------------+---+---+------+---+---+---++ |Faces of Bastions | 22| 25| 28 | 30| 33| 35|| +-----------------------+---+---+------+---+---+---++ |Capital of Ravelins | 25| 28| 30 | 35| 38| 40|| +-----------------------+---+---+------+---+---+---++

+-----------------------++---------------++-------+-------+ | || Little. || Mean. | Great.| +-----------------------++---+---+---+---++---+---+---+---+ |Side of Polygon ||140|150|160|170||180|190|200|260| +-----------------------++---+---+---+---++---+---+---+---+ |Length of perpendicular|| 20| 21| 23| 25|| 30| 31| 25| 22| +-----------------------++---+---+---+---++---+---+---+---+ |Faces of Bastions || 40| 42| 45| 47|| 50| 53| 55| 60| +-----------------------++---+---+---+---++---+---+---+---+ |Capital of Ravelins || 45| 50| 50| 52|| 55| 55| 60| 50| +-----------------------++---+---+---+---++---+---+---+---+

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 the TABLE.

TABLE _of capitals and flanked Angles_.

+---------------------------+------+-----+-----+-----+-----+ | Polygons. | IV | V | VI | VII | VIII| +---------------------------+------+-----+-----+-----+-----+ |The flanked angles in the | deg. | | | | | |3 sorts of fortification. | 64 | 76 | 84 | 90 | 95 | +---------------------------+------+-----+-----+-----+-----+ | |toises| | | | | |Capital for the great sort.| 46 | 49 | 51 | 52 | 53 | +---------------------------+------+-----+-----+-----+-----+ |Capital for the mean sort. | 42 |44¹⁄₂|46¹⁄₂|48¹⁄₂| 50 | +---------------------------+------+-----+-----+-----+-----+ |Capital for the small sort.| 39 |41¹⁄₂|42¹⁄₂| 45 | 46 | +---------------------------+------+-----+-----+-----+-----+

+---------------------------+-----+-----+-----+-----+ | Polygons. | IX | X | XI | XII | +---------------------------+-----+-----+-----+-----+ |The flanked angles in the | | | | | |3 sorts of fortification. | 97 | 99 | 101 | 103 | +---------------------------+-----+-----+-----+-----+ | | | | | | |Capital for the great sort.|54¹⁄₂|56¹⁄₂| 58 | 59 | +---------------------------+-----+-----+-----+-----+ |Capital for the mean sort. | 51 |52¹⁄₂| 54 | 54 | +---------------------------+-----+-----+-----+-----+ |Capital for the small sort.|47¹⁄₂|48¹⁄₂| 50 |50¹⁄₂| +---------------------------+-----+-----+-----+-----+

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, the _French 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. This engineer acquired great reputation during the several sieges which he assisted in conducting under Louis XIII. His system has been improved upon by _Alain 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, the _French method_. Others call it the _Compound System_, or _Systeme 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 already mentioned the principal feature, in his method.

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._ The _great_, the _mean_, and the _little_.

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 or _rechutes_ which might be made: he invented arched bastions that were bomb proof, which he called _tours bastionnées_, or _towers 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 method of 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 called _ordre renforcé_, the _reinforced 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 the _ordre 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; the _great_, whose exterior side contains 200 toises; and the _little_, 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: