FORTIFICATION. 
lar, when the enclosed area is of such a 
form, as can be inscribed in some regular 
figure; such as a triangle, a rectangle, a 
circle, or an ellipsis : observing that such 
figure should, in a manner, fit the town, &c. 
it is intended to protect. It is usual to 
divide the perimeter, or whole outline of 
the figure, when it is either of the two lat- 
ter forms, into as many faces, or portions, 
as may admit of suitable defences in either 
of the three systems already detailed. The 
number of faces must be regulated as well 
by the form, as by the extent of the figure. 
Small circles may be divided 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 order to reduce the exte- 
rior lines of defence within due bounds ; 
so that every part of each face may be 
within musquet shot of those parts whereby 
„ it is flanked, or defended. Whenever this 
fundamental principle is disregarded, the 
plan will be proportionally weaker, accord- 
ing to the undue 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 outworks ; 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 sys- 
tem ; 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 lateral faces being 
strengthened with ravelines, lunettes, te- 
nailles, or other works, all these are evi- 
dently regular members of a perfect whole, 
and when duly combined, according to the 
rules of art, form a complete and regular 
defence, founded on approved systems. 
When the number of faces has been ad- 
justed and laid down, it is proper to decide 
whether the works are to be planned out- 
wards, 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 interior 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 fortifica- 
tion, the several lines, describing the outer 
part of each rampart, exhibit the situation 
of a semicircular projection of masonry, 
called the cordon, which is, with few ex- 
ceptions, made, at the top of their respec- 
tive facings of stone, brick, &c. called reve- 
tements. The line thus following the direc- 
tion of the cordon, as it proceeds along the 
works, is called the principal. 
A reference to fig. 1, Plate Fortification, 
will illustrate the foregoing description. The 
half of a hexagon, or polygon of six equal 
sides, is selected, as being the most appropri- 
ate to this occasion. The line A D, is the dia- 
meter of the circle ; which circle having 
been divided into six equal parts, each 
equal to the radius, or semidiameter, A E, 
or E D, gives the faces formed by the pas- 
sage of the rays B E, and C E, through the 
points of equal division B and C. Let us 
suppose the fortification to proceed in- 
wards i in such case the lines A B, B C, 
C D, will be termed exterior 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 A B, 
B C, CD, and D C clear, the principal 
would have been projected outwards, and 
the lines A B, B C, CD, would then have 
been termed the interior side. The former 
mode is in use when the exterior of the de- 
fences is first marked out, and has its sepa- 
rate mode of formation ; and the latter is 
adopted where the interior of the works is 
established by any pre-existing circum- 
stances, such as fortifying an old town, &c. ; 
and proceeds on a suitable plan of projec- 
tion. The two modes correspond perfectly, 
giving the same angles and proportions; 
the former on a diminished, the latter on 
an extended scale. 
The interior lines F G, G II, H I, form 
parallel faces with those on the exterior 
lines A B, B C, C D. If it were required 
to fortify outwards, they would be the 
bases of their several defences respectively, 
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 fa- 
miliar. 
To fortify inwards from an exterior line . — 
Let the exterior line B C, be 180 toises, 
(each toise being one fathom, or six feet,) 
bisect it in d, and draw the perpendicular 
d 8 equal to one sixth of the exterior line 
B C, 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 
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