A B is the slope of the banquette.
B C head of the banquette, or place where the men stand to deliver their fire.
C D the interior slope of the parapet.
D E superior slope of the same.
F G the berme, or place left to prevent the parapet from washing down into the ditch.
G H the scarp or interior wall of the ditch.
H I the bottom of the ditch.
I K the counterscarp.
L M N the glacis, which, except the abatis near the ditch, is left free and open, so as to expose the assailants to the fire from the parapet.
The proportions and angles of all the lines given are fixed according to mathematical rules.