PARAPET, in Fortification, is generally an embankment of earth which is formed either on the natural ground or on the upper surface of the rampart of a fortress or outwork. In the latter case the parapet rests on that part of the rampart which is nearest to the exterior of the work, the terreplein, or nearly level part on the interior side, being occupied by the artillery or left free for the movements of the defenders. Parapets of brick or stone are sometimes constructed for works which are masked by others in their front, or on heights, or on the sea-coasts; but in other circumstances they would be improper, because the splinters detached from such materials by the enemy's shot aro dangerous to tho defenders, whereas the shot sinks into earth without doing further mischief.
The height of a parapet above the ground, or above the terreplein of a rampart which it surmounts, is about 7,1 feet, in order that it may effectually cover the defenders behind it. In its mass are cut Abe embrasures through which the guns are fired ; and a banquette, or step, about 3 feet high and 4 feet broad is formed, usually of earth, at its foot, on the interior side, in order to enable men, by standing on it, to fire over the upper surface. Tho form of a transverse section of a rampart, surmounted by a parapet, is represented in fig. 2, BaszioN; the parapet with its banquette being that which occupies, ou the right hand side of the figure, rather less than the upper half of the space between the dotted lines. .
The exterior face of a parapet of earth is generally formed in a plane making an angle of 45 degrees with the horizon, in order that the earth may stantT unsupported; the superior surface, which varies in breadth from 3 feet to 25 feet according to the nature of the shot which it is intended to resist (from musket bullets to the balls discharged from the heaviest ordnance), has its exterior crest or edge lower than the other by about one-sixth of the breadth of that surface. It is recom mended that the depression of the slope should not bear a greater proportion to the breadth, lest the upper part of the parapet should by its acuteness be weakened ; but the general rule is that the plane of the superior slope should, if produced, meet the counterscarp line of the ditch in front, in order that the enemy, at the time of an assault, and when detained by the obstacles there, may be completely exposed to the fire of musketry from the parapet. The interior face of the
parapet is frequently formed in a plane pa.ssing through the crest, and, at the terreplein of the banquette, or at the foot of the parapet if there is no banquette, deviating from a vertical plane passing through the same crest about one-third of the height of the slope. By this'inclina don the earth, when reacted with faseines or sods, and even without say revetment, will support itself for a time, while a man, by leaning a little forward, is enabled without inconvenience to fire over the parapet.
Occasionally parapets of field-works have been formed with the earth obtained by excavating the ground in the interior ; and, in this case, the crest of the parapet may be only 3 or 4 feet above the exterior ground. Such a construction is admissible, however, only when the site of the work is several feet higher than the ground which the enemy may occupy, since otherwise the defenders, except when close behind the parapet, would be exposed to his fire. Again, should the ground about the spot to be fortified be higher than that spot, the crest of the parapet must have a greater height than 74 feet, in order that the defenders may be sufficiently covered by it : but in general the parapets of field-works cannot be raised more than 14 feet above the ground; since a man can scarcely throw earth with a spade to a greater height than 7 feet, and a greater height than 14 feet would require, above ground, more than two rows of shovellers, one row 7 feet above the other, besides one row, or two rows, at an equal interval in the ditch ; and it is seldom that the numerical strength of a working party is sufficient to allow such a disposition to be made.
The earth used for forming the parapets should be as free as possible from stones or gravel, or these should be put into the centre of the mass, in order to avoid the accidents which might arise from the dis persion of the stones when shot or shells strike ; and the slopes, as well as the banquettes, when time permits, should be covered with turf.