Encyclopaedia Britannica > Volume 7, ETM-GOA

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FORTIFICATION.
with loop-holes were made at proper diftances, in or¬
der to fcreen the defenders againft the arrows of the
affailants : but finding that, as foon as the enemy got
once clofe to the walls, they could from no part be
difcovered or repulfed; for this reafon they added fquare
towers at proper diftances from each other, fo that
every part of the wall might be defended by the adja¬
cent fides of the towers. However, this manner of
inclofing of towns was found to be imperfeft, becaufe
there remained ftill one of the faces of the towers
which fronted the field that could not be feen from any
other part, and therefore could not be defended. To
remedy this, they made the towers round inftead of
fquare, imagining this figure to be the ftrongeft to re¬
fill the battering engines, as likewife to be better de¬
fended from the other parts of the wall.
Notwithftanding the fuperiority of this method a-
bove the former, there remained yet a part of thefe
towers unfeen and incapable of being defended; which
made them change the figure of the towers again ;
that is, they made them fquare as before ; but, inftead
of prefenting a face to the field as formerly, they pre-
fented an angle ; by this means they effedtually found
out fuch a difpofition of their works, that no part
could be attacked without being feen or defended by
fome other part.
This laft method was in ufe a long while; and would
in all probability have continued to this day, if gun¬
powder had not been found out: but the violence of
the guns and mortars foon convinced the world, that
fuch towers and walls were but a weak defence againft
thefe thundering engines; and befides, as the nature
of the attack was entirely changed, it was alfo necef-
fary to change that of fortifying likewife.
From that time ramparts were added to the walls,
the towers enlarged into baftions, and all forts of out¬
works have been added, fuch as ravelins, counter¬
guards, horn and crown works, and others of the like
nature, in order to render the defence in fome meafure
equivalent to the attack.
Notwithftanding all the improvements which have
been made in the art of fortifying fince the invention
of gun-powder, that of attacking is ftill fuperior to it:
engineers have tried in vain to render the advantages of
a fortification equal to thofe of the attack; the fupe¬
riority of the befiegers fire, together with the greater
number of men, obliges generally, fooner or later, the
befieged to fubmit.
The greateft improvement made in the art of at¬
tacking happened in the year 1697, when M. Vaukan
made firft uie of ricochet-firing at the fiege. of Ath,
whereby the befieged.placed behind the parapets were
as much expofed to the fire of the befiegers as if there
had been none ; whereas, before, they had been fe-
cure as long as the parapet was not demoliftied : and
the worft is, that there can be no remedy found to
prevent this enfilading, without falling into inconve-
niencies almoft as bad as thofe which we endeavour to
avoid.
Fortification is either regular or irregular. Re¬
gular fortification, is that built in a regular polygon,
the fides and angles of which are all equal, being com¬
monly about a mulket-fhot from each other. Irregular
fortification, on the contrary, is that where the fides
and angles are not uniform, cquidiftant, or equal ;
363
which is owing to the irregularity of the ground, val- Vauban's
leys, rivers, hills, and the like. Method.
Sect. I. Of Regular Fortification.
Althouuh authors agree as to the general form in
the prefent manner of fortifying, yet they moftly differ
in particular conftruftions of the parts. As it would
be both needlefs and fuperfluous to treat of all the dif-
fetjjnt methods hitherto propofed, we {hall contept
ourfelves with explaining thofe only which are moll
efteemed by the bell judges, and have been moftly put
in practice. •
Confrullion of M. Vauban's Method.
This method is divided inio little, mean, and great ;
the little is chiefly ufed in the conftru&ion of citadels,
the mean in that of all forts of towns, and the great in
particular cafes only.
We {hall give the conftrudtion of the mean, as being p*atei
moft ufeful ; and refer the reader to the table hereaf- ^^^*
ter, for thofe dimenfions which are different in thefe fe-
veral fortifications.
Infcribe in a circle a polygon of as many fides as the
fortification is defigned to have fronts ; let AB be one
of the fides of half an hexagon, which bifedl by the
perpendicular CD ; divide half AC of it into nine
equal parts, and one of thefe into ten others; then
thefe divifions will ferve as a fcale to conftruft all the
parts of the fortification, and each of them is fuppo-
fed to be a toife or fathom, that is, fix French feet;
and therefore the whole fide AB is fuppofed to be 180
toifes.
As the dividing a line into fo many equal parts is
troublefome and tedious ; it is more convenient to have
a fcale of equal parts by which the works may be con-
ftrufted.
If therefore, in this cafe, the radius is taken equal
to 180 toifes, and the circle deferibed with that radius
being divided into fix equal parts, or the radius being
carried fix times .round, you will have an hexagon in-
feribed; AB being bifefted by the perpendicular CD
as before, fet off 36 toifes from C to D, and draw the
indefinite lines ADG, BDF ; in which take the parts
AE, BH, each equal to 50 toifes; from the cen¬
tre E deferibe an arc through the point H, meeting
AD in G, and from the centre H deferibe an are
through the point E, meeting BD in F ; or which is
the fame, make each of the lines EG, HF, equal to
the diftance| EH ; then the lines joining the points
A, E, F, G» H, B, will be the principal or outline of
the front.
If the fame conftrudlion be performed on the other
fides of the polygon, you will have the principal or
outline of the whole fortification.
If, with a radius of 20 toifes, there be deferibed
circular arcs, from the angular points B, A, M, T,
and lines are drawn from the oppofite angles E, H,
&c. fo as to touch thefe arcs, their parts ab, be. See*
together with thefe arcs, will reprefent the outline Of
the ditch.
Definitions.
1. The part FEALN, is called the baftion,
2. AE, AL, the faces of the baftion.
3. EF, LN, the flanks.
4. FG, the curtain.
Z z 2
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