Composed bastion, is when two sides of the interior polygon are very unequal, which also renders the gorges unequal; it may not improperly be called a forced bastion, being as it were forced into that form.
Deformed bastion, is when the irregularity of the lines and angles causes the bastion to appear deformed, or out of shape.
Demi-bastion, is composed of one face only, has but one flank, and a demi-gorge.
Double bastion, is that which is raised on the plane of another bastion, but much higher; leaving 12 or 18 feet between the parapet of the lower, and the foot of the higher; and is sometimes in the nature of a cavalier.
Regular bastion, is that which has its true proportion of faces, flanks, and gorges.
Irregular bastion, is that wherein the above equality of just proportion is omitted.
Barriers, in fortification, a kind of rails to stop the horse or foot from rushing in upon the besieged with violence. In the middle of this kind of defence there is a moveable bar of wood, which opens or shuts at pleasure.
Berm, is a little space or path, of 4 to 8 feet broad, between the ditch and the talus of the parapet; it is to prevent the earth from rolling into the ditch, and serves likewise to pass and repass. As it is in some degree advantageous to the enemy, in getting footing, most of the modern engineers reject it.
Bonnet, in fortification, is a sort of work placed before the saliant angle of the ravelin to cover it: it consists of 2 faces, parallel to the ravelin, or perpendicular to those of the lunette. They are generally made 10 fathom broad at the ends with a ditch of the same breadth, the covert-way 6, and the glacis 20 fathom.
Breach, is on opening or gap made in a wall or rampart, with either cannon or mines, sufficiently wide for a body of troops to enter the works, and drive the besieged out of it.