FORTIFICATION. 
that every out-work, as it is placed more 
distant from the principal, must have a less 
elevation from the terre-pleine, or level of 
the area, on which the walls of the princi- 
pal are founded. Thus we find, that a line 
drawn from the foot of the glacis g, at <t> 
opposite to the flanlsed angle of the bastion 
C, in the horn-work M, carried through the 
centre aH the way up to E, which is the 
centre of the polygon, should graze the 
crests or inner summits of all the parapets 
standing in that line : this is called the 
defilement of the ramparts. By such a 
construction it must be obvious, that every 
added work is a screen to, but is com- 
manded by that within it : thus, the bastion 
C, in the crown-work M, is a screen to the 
raveline N, and that again to the curtain 
u v ; while the intrenchments f f, corres- 
pond in height with the flanks of the horn- 
work, so as to be under the command of 
the raveline, though they command all that 
portion of M which is in their front ; and 
would continue to do so until the besiegers 
should construct batteries in the gorges of 
the bastions b, C, b, or elsewhere, and render 
ff untenable. 
The angle C, of bastion 4, is covered by 
the counterguard 7, which not only has that 
effect, but protects the adjacent tenailion 
R, and can plonge upon the adjoining flank 
of the crown-work M. As a still further 
covering to the bastion 4, a fleche 9 is ad- 
ded, parallel to the counterguard 7, at the 
foot of its glacis, serving to render the at- 
tack more tedious and difficult, by com- 
pelling the besiegers to commence their 
approaches at a greater distance, where 
they are more generally subject to the fire 
from the bastions, & c. of the crown-work. 
The fleche (i. e. arrow-head,) should pro- 
perly'extend equally each way, having both 
faces alike, but that is not of any moment, 
and might have a second glacis ; it is con- 
nected with the counterguard, or with the 
crown- work, or with the tenailion, by means 
of a sortie, or winding passage cut through 
the glacis, or by a caponnier, as in the 
plate, intercepted- with traverses* which 
will be duly explained when treating of the 
co vert- way. 
The raveline K is defended within by the 
redoubt L, surrounded by a dry ditch. 
This redoubt should not be too high, be- 
cause it would else serve to shelter the 
enemy in case they should succeed in si- 
lencing the faces of C 6, and m D, of the- 
corresponding bastions 4 and 5. The small 
work S is a lunette, which must be carried, 
or silenced, before the raveline can be 
breached in that part ; and, indeed, before 
any lodgment can be made opposite to the 
flanked angle D, of the bastion 5. The 
lunette must be lower than the raveline, 
from which it properly derives its defile- 
ment, as will be hereafter explained. 
The tenailion R is a very important con- 
junctive to the raveline K ; it, in fact, dou- 
bles its force on that side, and prolongs the 
battery of its other face ; it flanks the coun- 
terguard, and its direct fire is a great pro- 
tection to the demi-bastion b, on that side 
of the horn-work, as well as to the whole 
face of its raveline a ; it commands the 
fleche ; and being itself commanded by the 
raveline K, and by the face C 6, and the 
counterguard 7, cannot be occupied by an 
enemy while any of these three works re- 
main in force. 
With respect to the construction of tire 
counterguard, lunette, and tenailion, they 
are not upon any exact scale in proportion 
to the principal, as the raveline is, but 
though not perfectly arbitrary, their for- 
mations depend on some general rules, 
which should invariably be had in view. 
The counterguard is always placed on the 
counterscarp, its front immediately behind 
the glacis, and its rear, generally being a 
continuation of the revetement of the coun- 
terscarp, so that the passage lays along its 
terre-pleine, or battery. This kind of work 
may be of any extent, that is, it may pro- 
ceed from ravelir « to raveline without in- 
terruption ; or it may break off where it 
enters a lunette, a teoaillon, or a redoubt ; 
or it may be only formed of two parallels 
equal in length with the faces of tire bas- 
tion. On account of the number of men 
required for the defence of extensive out- 
works, counterguards are advantageously 
made hollow, having casemates covered 
with bomb-proofs, their parapets being solid 
masonry : their entrances, at each end, are 
secured by barriers and drawbridges ; and 
their walls may, in places, be pierced with 
loop-holes, through which musquetry may 
be discharged against assailants. 
Casemates are likewise made on each 
side of the posterns, or arched passages 
through the faces of ravelines ; there are 
always drawbridges and barriers in such 
situations, as also at the cuts through the 
lunettes, &c. which lead through the covert 
way to the esplanade, and are called sorties. 
The necessity for casemates must, gene- 
rally, depend on the quantity and distance 
of out-works from the body of the place : 
