FORTIFICATION. 483

from m to /; and from the points h, l, the flanks lik, Ip, are drawnparallel to the capital LO of the ravelin. There are sometimesredoubts made in the ravelin, such as in fig. 1. No. !. which isdone by setting off 16 toises from the extremities of the faces onthe semi-gorges from N to b, and from M to a ; and from thepoints b, a, the faces are drawn parallel to those of the ravelin ; theditch before the redoubt is six toises, and its counterscarp parallelto the faces.

Construction ofTenaiu.es.

A tenaille' is a work marie in the ditch before the curtins, theparapet is only two or three feet higher than the level ground of theravelin. There are three dilTerentsorts; the first are those, as infig. 3, which are made in the direction of the lines of defence,leaving a passage of three toises between their extremities and theflanks of the bastions, as likewise another of two in the middle fora bridge of communication to the ravelin. The second sort arethose, as in tig. 4. Their faces are in the lines of defence, and Hitoises long, besides the passage of three toises between them andthe flanks outlie bastion ; their flanks are found by describing arcsfrom one shoulder of the tenaille as centre through the other, or onwhich are set 10 toises for the flanks desired. The third sort-arethose as in fig. 5. Their faces are Hi toises, as in the second sort,and the flanks are parallel to those of the bastions. The use oftenailles in general, is to defend the bottom of the ditch by a graz-ing fire, as likewise the level ground of the ravelin, and especiallythe ditch before the redoubt within the ravelin, which c;tn be de-fended from no where else so well, as from them. The first sortdo not defend the ditch so well, as the others, as being too oblique adefence; but as they are not subject to be enfiladed. M. Vaubanhas generally preferred them in the fortifying of places, as may beseen in the citadel of Lille , Landau, New Brisac, and in manyother places. The second sort defend the ditch much better thanthe first, and add a low flank to those of the bastions ; but as theseflanks are liable to be enfiladed, they have not been much put inpractice. This defect might however be remedied, by makingthem so as to be covered by the extremities of the parapets of theopposite ravelins, or by some other work. As to the third sort,they have the same advantage as the second, and are likewise lia-ble to the same objections; for which reason, they may be usedtvith the same precautions which have been mentioned in the se-cond. Tenailles are esteemed so necessary, that there is hardlyany place fortified without them; and with reason: For whenthe ditch is dry, the part behind the tenailles serves as a place ofarms, from which the troops may sally, and destroy the works ofthe enemy and the ditch, oppose their descent, and retire with safe-ty ; and the communication from the body of t he place to the rave-lin becomes easy and secure, which is a great advantage; for bythat means the ravelin may be a much better defence, as it can beApplied with troops and necessaries at any time. And if the ditchis wet, they serve as harbours for boats, which may carry outarmed men to oppose the passage over the ditch wheneverthey please; and the communication from the tenailles to the^vel'm, becomes likewise much easier than it would be without

diem.

Construction of Lunettes.

big. 1. No. 2. Lunettes are placed on both sides oftho ravelin,*hch as B, to increase the strength of a place: they .are construct-ed, by bisecting the faces of the ravelin w ith the perpendicular~N; on which is set oil' 30 toises from the counterscarp of the‘“teh, for one of its faces; the other face, I’N, is found by makingme semigorge, TP, of 25 toises; the ditch before the lunettes is 12sojses, the parapet three, and the rampart eight, as in the ravelin.1 here is sometimes another work made to cover the saliant angle ofravelin, such as A, called bonnet, whose faces are parallel tovnose of the ravelin, and when proffuced, bisect those of the lu-nettes; the ditch before is 10 toises. There are likew ise lunettes,s uch asD in fig. 0, whose faces are drawn perpendicular to those

tiie ravelin, within a third part from the saliant angle ; and their* SeiTU -gorges are only 20 toises. These kinds of works may make a&°od defence, and cost no very great expence; for as they are sonear the ravelin, the communication with it is very easy, and one^iiuot well be maintained till they are all three taken.

Construction of Tenaiilons.

L No, 3. Produce the faces of the ravelin beyond the

counterscarp of the ditch, at a distance MN of 30 toises, and takeon the counterscarp of the great ditch 15 toises from the re-enteringangle q to p, and draw N p; then pN M q will be the tenailles re-quired ; its ditch is 12 toises, that is, the same as-that ofllie ravelin.Sometimes a retired battery is made in the front of the tenaiilons, asin B ; this battery is 10 toises from the front to which it is parallel,and 15 toises long. Retrenchments are commonly made in thetenaiilons, such as O; their parapets are parallel to the fronts MN,and bisect the sidepN ; the ditch before the retrenchment is threetoises; and there is a banquette before (he parapet next to the ditchof about eight feet, called berm ; which serves to prevent theeartii of the parapet {which seldom has any revetment) from fallinginto the ditch.. The ravelin, before which tenaiilons are construct-ed, mutt have its saliant angle much greater than the former con-struction makes them ; otherwise the saliant angles of the tenail-lons become too acute; for which reason we made the capital nithis ravelin 45 toises, and the faces terminate within three toises ofthe shoulders. •

Construction of Counter-guards.

When the couiitcrguard is placed before the ravelin, fig. 7, setoff 40 toises on the capital of the ravelin from the saliant angle A tothe saliant angle B, of the counterguard ; and 10 from C to 17; onthe counterscarp of the ditch. When the couiitcrguard is beforethe bastion, such as in fig. 8, its saliant angle F is 50 toises from thesaliant angle E of the bastion, and the breadth near the ditch of theravelin 10 toises as before. The ditch before the couuterguards is12 toises, and its counterscarp parallel to the faces. Couuterguardsare made before the ravelin on some particular occasions only ; butare frequently constructed before the bastions, as covering theflanks wonderfully well. Some authors, as Mr. Blondel'and"Mr.Coehorn, will have them much narrower than they are here.

Construction of Horn-works.

Fig. 1. No. 4. Produce the capital of the ravelin beyond thesaliant angle A, at a distance AB of about 80 toises; draw I)BE atright angles to AB ; in which take BD, BE, each equal to 55 toises;and on the exterior side DE, trace a front of a polygon in thesame manner as that of the body of the place, making the perpen-dicular BF 10 toises, and the faces 30. The branches Da, Ed, ofthe horn-work, when produced, terminate on the faces of the bas-tions, within five toises of the shoulders. The ditch of the horn-work is 12 toises, and its counterscarp parallel to the branches; andin the front terminates at the shoulders, in the same manner as thegreat ditch before the bastions. The capital of the ravelin beforethe front of the horn-work is 35 toises, and the faces terminate onthe shoulders, or rather two or three toises beyond them : and theditch before the ravelin is eight toises. Retrenchments arc some-times made within the horn-works, such as S, S; which are con-structed by erecting perpendiculars to the faces of the ravelins,w ithin 25 toises of their extremities. This retrenchment, like allothers, lias a parapet turfed only with a berm of fight feet beforeit; as like-wise a ditch from three to live toises broad. When ahorn-work is made before the bastion, (he distance, No. 5, ofthe front from the saliant angle of the bastion is 100 toises, and thebranches terminate on the faces of the adjacent ravelins w ithin livetoises from their extremities ; all the rest is the same as before.

Construction of Crown-Works.

From the saliant angle, A, fig. 0, of the ravelin, as a centre, de-scribe an arc of a circle with a radius of about 120 toises, cuttingtin-capital of the ravelin produced at C ; from t)ie point C, set oil'the chords CB, CF, each ot them equal to 110 toises ; ami on eachof which, as an exterior side, construct a front of pohgon of thesame dimensions as in the horn-work ; that is, the perpendicularshould be 18 toises, the faces 30, and the brandies terminate on thefaces of the bastions within 25 toises of the shoulders. The ditchis 12 toises, the capital of the ravelins 35, and its ditch 8 ; that is,the same as in the horn-wojk. Sometimes the crown-work b madebefore tile bastion, as in fig. 10. The arc is described from thesaliant angle A of the 1 bastion, with a radius of 120 toises, as be-fore ; anil tbe brandies terminate on the faces of the adjacentravelins within 25 toises of their extfiemities-; the rest of the dimen-sions and constructions are the same as before. Horn-works, aswell as crown-works, are never made but when a large spot of

ground