FORTIFICATION. 



figure ; such as a triangle, a rectangle, a 

 circle, or an ellipsis : observing that such 

 figure should, in a manner, n't the town, 

 &c. it is intended 10 protect. It is usual 

 to divide the perimeter, or whole outline 

 of the figure, when it is either of the two 

 latter forms, into as many faces, or por- 

 tions, as may admit of suitable defences 

 in either of the three systems already de- 

 tailed. The number effaces must be re- 

 gulaied as well by the form, as by the ex- 

 tent of the figure. Small circles may be di- 

 vided into five or six faces ; moderately 

 extensive ovals may have six also; while 

 the more extensive circles and ovals will 

 require an additional face or more, in or- 

 der to reduce the exterior lines of defence 

 within due bounds ; so that every part of 

 each face may be within musket shot of 

 those parts whereby it is flanked, or de- 

 fended. Whenever thid fundamental prin- 

 ciple is disregarded, the plan will be pro- 

 portionally weaker, according to the un- 

 due prolongation of the faces, and the 

 consequent deficiency of mutual support. 



The several fronts of a fortification may 

 be all dissimilar, both in their proportions 

 and in their extent ; as also in the number 

 and construction of their several out- 

 works; yet the whole cannot be termed 

 irregular. Thus the two ends of a long 

 oval may be constructed on the second, 

 i e. the mean system ; while each of the 

 two long sides may be upon the third, or 

 great system. One end may have a horn- 

 work; the other a crown-work : the late- 

 ral faces being strengthened with rave- 

 lines, lunettes, tenailles, or other works, 

 all these are evidently regular members of 

 a perfect whole, and when duly combin- 

 ed according to the rules of art, forma 

 complete and regular defence, founded 

 on approved systems. 



When the number effaces has been ad- 

 justed and laid^ down, it is proper to de- 

 cide whether the works are to be planned 

 outwards, or inwards, from the line laid 

 down. In the former case much space is 

 gained by keeping all clear within that 

 line, which by this means becomes the in- 

 terior side : in the latter instance the line 

 becomes the exterior side, all the works 

 being raised within it, which considerably 

 diminishes the area within them. It is to 

 be remembered, that in laying down the 

 plan of a fortification, the several lines, 

 describing the outer part of each ram- 

 part, exhibit the situation of a semicircu- 

 lar projection of masonry, called the cor- 

 don, which is, with few exceptions, made 

 at the top of their respective facings of 

 stone, brick, &c. called revetements. The 

 line thus following the direction of the 



cordon, as it proceeds along the works, is 



called the principal. 



A reference to rig. 1, Plate Fortifica- 

 tion, will illustrate the foregoing descrip- 

 tion. The half of a hexagon, or polygon 

 of six equal sides, is selected, as being the 

 most appropriate to this occasion. The 

 line, AD, is the diameter of the circle ; 

 which circle having been divided into six 

 equal parts, each equal to the radius, or 

 semidiameter, AE, or ED, gives the faces 

 formed by the passage of the rays BE, 

 and CE, through the points of equal divi- 

 sion, B and C. Let us suppose the fortifi- 

 cation to proceed inwards : in such case 

 the lines AB, BC, CD, will be termed ex- 

 terior sides, and all the principal will be 

 formed within them; whereas, had it been 

 intended to cover more ground, and to 

 keep the whole of the area contained 

 within the lines AB, BC, CD, and DC, 

 clear, the principal would have been pro- 

 jected outwards, and the lines AB, BC, 

 CD. would then have been termed the in- 

 terior side. The former mode is in use 

 when the exterior of the defences is first 

 marked out, and has its separate mode of 

 formation ; and the latter is adopted, 

 where the interior of the works is estab- 

 lished by any pre-existing circumstances, 

 such as fortifying an old town, &c. ; and 

 proceeds on a suitable plan of projection. 

 The two modes correspond perfectly, giv- 

 ing the same angles arid proportions ; the 

 former on a diminished, the latter on an 

 extended scale. 



The interior lines FG, GH, HI, form 

 parallel faces with those on the exterior 

 lines AB, BC, CD. If it were required 

 to fortify outwards, they would be the 

 bases oftheir several defences respective- 

 ly, and the measurements would be taken 

 from them, in lieu of from the exterior 

 line. We shall proceed according to the 

 latter mode, it being the most common 

 and the most familiar. 



To fortify inwards from an ex tenor line. 

 Let the exterior line BC be 18u toises, 

 (each toise being one fathom, or six feet,) 

 bisect it in d, and draw the perpendicular 

 d8 equal to one sixth of the exterior line 

 BC, namely, 30 toises. Now from B draw 

 the line B v, passing through the point n\ 

 and from C draw the line C -u, intersecting 

 B v in n. Set off 50 toises from the 

 points B and C, on their respective lines, 

 which are called the lines of defence, giv- 

 ing B t and C iv for the faces of the two 

 bastions. With the opening t iv, measure 

 t v and iv u, on the lines of defence, to de- 

 termine their proper lengths, so as to give 

 MTjfor the length and position of the cur- 

 tain ; next draw the liaes t v and w v, ei- 



