A military dictionary

by William Duane

Line of defence, is the distance between the saliant angle of the bastion, and the opposite flank; that is, it is the face produced to the flank. Common experience, together with some of the greatest artists in fortification, unanimously agree, that the lines of defence may extend (though not exceed) 150 fathom. Some indeed will affirm, that as a musquet does not carry more than 130 fathom point blank, the angle of the bastion should be no further removed from its opposite flank. We agree that a musquet carries no farther point blank; but we are sure it will do execution, and kill, at 180 fathom. The enemy generally makes his breaches near the middle of the face; which if granted, the line of fire from the flank to the breach, scarcely exceeds 130 fathom; besides, the cannon of the flank does less execution upon a short line of defence than on a long one.

Line of defence fichant, is a line drawn from the angle of the curtain, to the point of the opposite bastion, which is not to exceed 120 fathom; and from the point of the curtain, and flank, to the face of the opposite bastion, which is to be defended. This line may not improperly be called in good English the butting flank, since it partly sees the opposite faces in reverse; and the shot from it, especially near the orillon, strike against the faces. Authors are numerous both for and against the fichant and rasant lines; we can only set down as a fixed rule, that the more powerful the active quality is, the more the passive must suffer; that in fortification the active quality is the fire, which discovers the assailants (who are the passive) going to attack the face of the opposite bastion; consequently, the more this active quality is augmented, by so much the more must the passive subjects suffer; and from thence we argue for the fichant flank, since it augments this active quality, by all the fire of the curtain added to the flank, which is the principal action in the art of defence.

Line of defence rasant, is a line drawn from the point of the bastion along the face, ’till it comes to the curtain, which shews how much of the curtain will clear, or defend the face. This line may very justly in our language be called the sweeping flank; because the shot as it were sweeps along the opposite faces. This line, as well as the fichant, has many supporters, and as many opponents. In our humble opinion, the line fichant is preferable to the line rasant.

Line of circumvallation. See [Siege]. See [Circumvallation].

Line of contravallation. See [Contravallation].

Line of counter-approach. See [Approaches].

Capital line, is an imaginary line which divides the work into two equal and similar parts, or a line drawn from the point of the bastion to the point where the two demi-gorges meet, &c.

Line of defence prolonged. In the square, and most polygons of the lesser fortification, you prolong the line of defence; but in the polygons of the greater and meaner, you draw a line from the angle of the opposite shoulder to the angle of the curtain, upon which you raise a perpendicular, which serves for the first line of the flank.

Names of the angles in a Fortification.

Angle of the centre, in a polygon, is formed by two radii drawn to the extremities of the same side, or from the centre, terminating at the two nearest angles of the figure.