by a bomb-proof
covering over head: this arrangement is termed a _casemate_.

Sometimes double ramparts and parapets are formed, so that the interior
one shall fire over the more advanced; the latter in this case is called
_a faussebraie_.

If the inner work be separated from the other it is called a
_retrenchment_[44] and if in addition it has a commanding fire, it is
termed, as was just remarked, a _cavalier_.

[Footnote 44: The term _retrenchment_ implies an interior work, which is
constructed within or in rear of another, for the purpose of
strengthening it; the term _intrenchment_, on the contrary, implies an
independent work, constructed in the open field, without reference to
any other adjoining work.]

The _capital_ of a bastion is a line bisecting its salient angle. All
the works comprehended between the capitals of two adjacent bastions is
termed a _front_: it is taken as the unit in permanent fortification.

Fig. 39 represents the ground plan of a modern bastioned front, of a
regular and simple form, on a horizontal site.

_A, A, A_--Is the enceinte, or body
of the place.
_B_--The bastions.
_C_--The main ditch.
_D_--The covered ways.
_E_--The re-entering places of arms.
_F_--The salient places of arms.
_G_--The demi-lune.
_H_--The demi-lune ditch.
_J_--The demi-lune redoubt.
_L_--The ditch of the demi-lune
redoubt.
_M_--The redoubt of the re-entering
places of arms.
_N_--The ditches of the redoubts.
_O_--The tenaille.
_P_--The double caponier.
_a_--The traverses.
_b_--The sortie-passages.
_c_--Stairs.
_d_--Cut in the demi-lune to flank
the redoubt of the re-entering
place of arms.

Fig. 40 represents a section through the line _mn'_ of the preceding
figure.

_A_--Is the rampart.
_B_--The parapet.
_C_--The ditch.
_D_--The scarp wall.
_E_--The counterscarp wall.
_F_--The glacis.
_G_--The covered way.
_H_--The terre-plain.
_J_--The parade.

Sometimes half embrasures are cut in the earthen parapet of a fort, so
as to sink the gun below the crest, and thus more effectually cover the
men from the enemy's fire.

But guns in embrasure have a far less extended field of fire than when
mounted in barbette; moreover, the embrasures present openings through
which an enemy may penetrate in an assault. Owing to these objections,
they are employe