Part 156

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.