To fulfil the first condition, parapets are usually made from 7 to 8 feet high. Not that this is the usual stature even of grenadiers, but because some additional height must be allowed for the protection of persons within the parapet from shot pitching over its crest, (a constant occurrence, as the course of every bullet is a curved line,) because the interior should be concealed from the view of a horseman, and also in anticipation of the reduction which the height of the parapet will suffer from exposure to continued fire. Where time presses, it may not be practicable to provide against these contingencies, and, in such a case, a 6-foot parapet must suffice.

The condition of thickness may be determined from the following table, which shows how deep each calibre of shot has been found to penetrate into an earthen bank, and what additional thickness of earth it is desirable in each case to allow:

:

From this results a rule easily remembered-that a parapet should have a foot of thickness for every pound-weight of the shot which it is intended to resist, from 6-pounders up to 18's. Parapets of permanent works, which, of course, must be prepared for any weight of metal, are usually from 18' to 20' thick.

It is plain that the earth, to form the parapet, may be either dug from the inside and thrown outwards, (Pl. I., figs. 1, 2, 3, 4, 6, and Pl. II., fig. 18,) or dug from the outside and thrown inwards, (as in Pl. I., figs. 7, 8, 9, 10, and Pl. II., figs. 20, 21.)

In the former case, protection will be most speedily obtained; for every foot in depth of earth that is dug and thrown out gives two feet of cover.* This protection, however, will be afforded only to troops actually standing in the excavation. * See figs. 1 and 2.

In so far cover-which we have said to be the first object in fortification is attained with great rapidity; the second object, inaccessibility, is not attained. The third, advantage in the use of troops and arms is, in some respects, rather lost than gained; for the defender, standing in a hole, is unfavourably placed both for watching his assailant's advance, and for a hand-to-hand struggle at the parapet. Hence such works are to be used where cover is the main object, or its rapid attainment of the greatest importance. Such cases are the trenches excavated to cover the advance of troops besieging a fortress; lines extending between two works of a stronger description to protect their communication with one another; breast-works thrown up on the spur of the occasion to block up a road, or assist the defence of a position, or to cover troops from artillery fire in the early part of a general action. One advantage of these trenches is, that their construction permits troops to charge over them without difficulty, whilst their fire is low and likely to be deadly. Such are the lines which the Sikhs seldom fail to commence instantly on occupying a position in front of an enemy, multiplying and strengthening them day by day when time is afforded.*

A good adaptation of such works in the field is on the crest of a hill descending in a slope towards the enemy. Here nature gives vantage, with, in some degree, difficulty of access; and a low parapet will suffice to cover from an enemy below, troops not only in the trench, but in its rear also.†

In soil affording but a shallow surface of earth that can be excavated, cover will be most rapidly attained by digging a trench outside and inside simultaneously. This, however, has the inconvenience of affording cover to the assailant when he reaches it.

In the second case, where the earth is dug from the outside, a greater amount of excavation is required to produce cover, but the excavation itself, or ditch, as it is called, becomes an obstacle to the enemy's advance-i. e., gives in greater or less degree inaccessibility. And in works deliberately executed, * See Note A, Sikh Intrenchments. + See fig. 3.

See figs. 5 and 19.

this is the usual construction, as the ditch affords facilities for the disposition of other obstacles to retard attack. Time pressing, however, the interior excavation is to be preferred, because, in whatever state of progress the work is interrupted, it gives some cover and benefit; whereas a half-finished work, with exterior excavation, will be useless to defenders, and may give good cover to the enemy.

It has been stated that the usual height of a parapet is 7 feet. As most works are intended for active as well as passive defence, it is obvious that some arrangement must be made to enable men to fire over such a height. For this purpose a step of earth is raised all along the inside of the parapet. 4 to 4 feet is the height over which men of average stature can fire a musket conveniently, and this fixes the height at which the step of earth must stand below the top of the parapet. This banquette, as the step is called, is usually made from 3 to 5 feet wide; and the slope to the rear, that it may be readily ascended, has a base equal to twice the height. Thus, in fig. 11,* which represents the usual form of a parapet with its ditch, as seen in profile and perspective, e f g is the banquette; f g the step itself, being called the tread of the banquette; and eƒ the slope of the banquette. The parapet a b c d is formed in three slopes-viz., an upper or top slope, an outer, and an inner slope, called technically, the superior, exterior, and interior slopes. There are certain general rules for the degree of inclination given to these slopes, which, as they depend on fixed reasons, do not vary much in their application to different works.

1

a b, the interior slope, is made very steep, that men may more conveniently stand close to it to fire over the parapet. Its usual slope is to the height; and as earth will rarely stand at such an angle, it becomes necessary to revet or face the slope with turf, timber, or other material. In permanent works, the interior of the parapet is often built perpendicular with masonry; but this is not desirable, as the splinters of masonry, struck by shot or shell, are destructive to the defenders.

The upper edge b is called the crest of the parapet, and

* Plate I.

generally the upper edge of any work or slope is called its crest.

bc is the superior slope. The more it is depressed towards the front, the more closely under the parapet can the ground before it be seen and defended. But if a very great depression be given to the slope, the crest b will become very sharp, and liable to rapid destruction. Hence, the depression usually given is of the breadth, and it is not advisable that it should exceed 1.

The exterior slope c d should not have a greater inclination than the soil will stand well at. In imaginary profiles, the base is usually made equal to the height.

The inner side of the ditch hi is called the escarp, and the outer side k the counterscarp. The steeper these are, the greater obstacle will the ditch be to an enemy. Hence, in permanent works, unless the ditch be full of water, both escarp and counterscarp are always walls of masonry. Sometimes a level path d h is left between the parapet and ditch. This is called a berm. It is necessary in some soils to prevent the earth of the parapet from slipping into the ditch, and it is a great convenience to the working parties when forming the parapet. But it is also too convenient as a landing for

assailants.

Sometimes a work called a glacis (k) is thrown up on the outside of the ditch, descending outwards in a gentle slope to the level of the country, or plane of site, as it is technically called. The glacis covers the lower part of the inner works from the enemy's fire; and when the edge of the counterscarp would otherwise be below the range of fire, the sloping rise of the glacis serves to bring it and the whole of the ground adjoining the outside of the ditch under the observation and fire of the parapet.

Where the parapet is thrown up from interior excavation, the banquette will be represented by a step cut in the outer side of the trench, or left like a berm between trench and parapet. Fig. 1 shows the least amount worth noticing of cover for troops; figs. 2 and 3, better cover, though also from * See figs. 2, 3, 4, 5.

interior excavation. Fig. 6 represents the minimum of cover for guns; figs. 7 and 8, parapets thrown up from outward excavation for defence against musketry; figs. 9 and 10, for defence against artillery. When no great thickness of parapet is required, and time is afforded, it may be desirable to increase the inaccessibility of the work by deepening the ditch, beyond what is needed to give earthfor cover.* The additional earth may be used in raising the parapet to a greater height, and the ascent to the banquette may be broken into two or more steps.

In nearly all the works of a permanent fortification, the parapet is raised on a terrace or bank of earth, sufficiently wide to afford space for the movements of the defenders and the working of their artillery. This bank is called the Rampart. It gives greater command to the works, where there are several lines enabling the interior line to overlook, and possibly to fire over, those which are exterior to it. Its height, usually protected by a lofty masonry escarp, renders surprise difficult, whilst it covers buildings within the fortress from direct fire. The level terrace of the rampart is called its Terrepleine, and the slope which terminates it on the inner side is the Interior slope of the Rampart. As this is usually steep, roads up it are made at intervals, with a gentle inclination, for the convenient ascent of troops and guns. Such roads are termed Ramps.

It has been explained how infantry are enabled to fire over a 7 foot parapet, by the aid of the banquette; it remains to be shown how artillery fire can be directed from behind a similar parapet. The height of a gun's muzzle varies from 2' 6" to 3' 9". It is clear, therefore, that either the gun must be raised so as to fire over the parapet, or the parapet must be cut down so that the gun shall fire through it.

The former method is carried out in two ways. Sometimes the gun and its carriage are mounted on a frame of massive timber, so high that the muzzle clears the crest of the parapet. The timber frame is fitted with trucks or wheels, moving on a semicircular rail, so that the fire of the gun can be directed to right, left, or front, whilst the gunners remain covered by the

* See fig. 7.