FORTIFICATION.

485

OF IRREGULAR FORTIFICATION.

Irregular Fortification is that whore the sides and anglesaie not uniform, equidistant, or equal; owing to the irregularity■of the ground, lulls, valleys, rivers, and the like. The most es-sential principle in fortification consists in making all the fronts of aplace equally strong, so that the enemy may find no advantage inattacking either of the sides. This can happen no otherwise in aregular fortification situated in a plain or even ground : lint asthere are hut few places which are not irregular either in theirworks or situations, and the nature of the ground may be such asmakes it impracticable to build them regular without too great ex-pence ; it is so much the more .necessary to shew in what consiststhe strength or weakness of a town irregularly fortified, so that theweakest part mav be made stronger bv additional outworks ; aslikewise, if such a place is to he attacked, to know, which is thestrongest or weakest part.

Construction of an Irregular Place in an openCountry.

If the place to be fortified i- an old town inclosed by a wall orrampart, as it most frequently happens, the engineer is to consi-der well all the different circumstances of the figure, situation,■and nature, of the ground; and to regulate his plan accordingly,so as to avoid the disadvantages and gain all the advantages pos-sible; he sJaohIcI examine, whether by cutting off some parts of theold wall or rampart, and taking in some ground, the place can bereduced into a regular form, or nearly so; for if that can be donewithout increasing the expence considerably, it should by nomeans he omitted.- Old towns have often-towers placed from dis-tance to distance, as Douav, Tournay , and many other places,which are generally made use of, and mended when it may hedone. If there be a rampart without bastions or towers, it must be■Well considered whether bastions mav not be added, or if it is notbetter to make only some outworks ; if the ditch about this ram-part is not too wide and deep, it would be advantageous to makedetached bastions ; otherwise ravelins and counterguards mu-.tbeconstructed. Special care must he taken to make all the sides ofthe polygon as nearly equal as possible, and that the length of thelines of defence do not exceed the reach of a musket-shot; hut ifthat cannot be clone, those sides which are on the narrowest partshould be made the longest. If some of the sides be inaccessible°r of very difficult approach, either on account of some precipice,marshy ground, or inundation, they may be made much longerthan the others which are easy of access, and the flanks need nothe so large as the rest; by doing so some expence will be saved,Which may be used in making the other sides stronger by addingmore outworks. There are few situations but what are more ad-vantageous in some parts than in others; it is therefore the busi-ness of an engineer to distinguish them, and to render those sidesstrong by art which are not so by nature. If the situation he low■and watery, lunettes cr tcnaillons, and such other small outworks,should be constructed ; because they are not of any great expence,and may make a very good defence. But if one side of theplace only be low, and running water is to be had, a second ditchand-covert-way with lunettes may be made, by observing, that ifme first glacis is made to slope, so as to become even with themvel of the water in the second ditch; or if the water can beswelled by means of dykes or sluices, so as to overflow the bestpart of the glacis, it should be done : for by doing this these workswill be able tp make very good defence, since the besiegers will find** a difficult matter to lodge themselves upon this glacis; whichc annot be done but within a few toises of the first covert-way,where the besieged are ready to receive them, and to destroy their'J'R'ks with great advantage ; whereas the enemy cannot supportJ eir workmen but from the second covert-way, which is too far

I to he of any great service to them- But if the situation be0r y. without any water about it, caponiers should be made in the8 r eat ditch, from the curtins to the ravelin, and batteries raised

II the entrance of the ditch before the ravelin, whose parapet

slope off into a glacis, so as to afford no cover for the enemy1 hind them. Arrows and detached redoubts are likewise verProper to be used in such a case ; and sometimes horn or crown' 0r ks, if ff should be thought convenient; but these works shouldCvcr he constructed without an Absolute necessity, cither to oc-

V °L. II—no. 88.

cupy a spot of ground which might he advantageous to the enemy,or to cover some gate or entrance in the town ; for they are of greatexpence, and their defence seems not to be answerable to it. Mostof the places in Flanders are fortified with horn-works, such asYpres, Tournay , Lille, and others. If the place to be fortified isnew, and the situation will not admit of a regular construction,particular care must be taken in choosing such a spot of ground asis most advantageous, and least liable to any disadvantages eitherin the building or in maintaining it. All hills or rising groundsshould be avoided, which might command any part of the works ;marshy grounds, because such situations are unwholesome; orlakes and standing waters for the same reason, excepting a lake isor may be made navigable. Good water should be had eitherwithin the place or near it, for it is absolutely necessary for men andcattle: the air should he wholesome; otherwise the continual sick-ness that may reign in such a place might prevent people fromcoming to live in it, and the garrison would not be in a conditionto defend themselves as they ought to do. In short, all the dif-ferent circumstances attending such an undertaking should be ma-turely considered before a resolution is taken to fortify any place.When a situation is fixed upon, the next thing to be considered is,the bigness of the town and the number of its outworks ; whichmust absolutely depend upon the consequence such a pilace'is ofto a nation. If it is only to guard a pass or entrance into a coun-try, it need not he so large : but if it is to be a place either to pro-mote or to protect trade, it should he large and commodious;the streets should be wide, and the buildings regular and conve-nient. As to what regards the fortification, its construction shoulddepend on the nature of the situation, and the number of workson the funds or expence a prince or nation will be at; which,however, ought to he according to the benefit arising from such aplace: for as such undertakings are of very great expeuce, anengineer cannot be too sparing in his works ; on the contrary, thegreatest a-conomy should be used both in regard to the number ofworks and to their construction. The body of the place may haverevetments quite up to the top, or only in part, and the restturfed ; hut as to the outworks they should have half-revetments,or they may he made with turf only ; as being not so necessaryto prevent the place from being surprised, which may neverthe-less make a good defence. Plate LXXIII. fig. 5, is the plan of anoctagon, one-half of which is similar and eoual to the other half.The exterior sides are each 180 toises, and the works are con-structed according to our method ; but because the sides AB, EF,are weaker than the rest, we have added tenailles, redoubts in theravelins, and lunettes, to render them nearly equal in strengthwith the others ; and if counter-guards were made before the bas-tions A and B, it would effectually secure that front. Instead oflunettes, any other works may be made, as may be thought con-venient and according to tiie nature of the ground. If it shouldbe judged necessary to add other'outworks to the ravelins all roundthe place, care must be taken to add likewise more to the frontsAB, EF, in order to render the advantages and disadvantages ofattacking on cither side equal.

Construction of an Irregular Fortification on a IIillor Rock.

In the construction of such places, care must be taken that noneighbouring bill commands any part of the works. The townshould always be built on the highest part; but if it should bethought more convenient to place it lower, then the upper partmust be fortified with a fort. The situation should be made asnearly level as possible, by removing the earth from some placesto fill up others ; and if it cannot w ell be levelled without ex-traordinary expence, works must be made on the highest part, soas to command and protect the lower. The works ought to oc-cupy alt the upper part of the hill ; but if it should be too exten-sive to be all inclosed, or so irregular as not to be fortified withoutgreat inconvenience, the parts which fall without should be fortifiedwith some detached works, and a communication with the placemust be made either above or below the ground. There shouldbe no cavity or hollow roads within cannon-shot round about theplace, where the enemy might be able to approach under cover.If there be a spring near the top of the hill, it should be inclosedin the fortification ; or if that cannot be done, by some work orother; for there is nothing more necessary, and at the same lime

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