is readily moved on as the trench advances. The usual size. is 6' by 4', with 9" interval between the two gabions. It has been found that, by giving the sap-roller a slight bulge in the middle, like that of a barrel, it is much more readily turned when the sap is required to form an angle.

2d, Fascines are faggots of brushwood. To make them conveniently, form trestles by driving pairs of stakes into the ground-St Andrew's cross-wise-at about 3' interval; lay the twigs and rods on the trestles till there are enough of them for a faggot of the thickness required; press or choke them hard together, and bind them at intervals with withes or string. The choking is accomplished with a tool which consists of a piece of chain joining two hand-spikes. The chain is cast round the faggot, and two men, by bearing on the hand-spikes, choke it hard, whilst a third binds. The choker is then transferred to another place for another binder, and so to the end of the fascine for every 12 or 18 inches of its length. Fascines are used in revetting parapets and embrasures; † in forming dams, and filling wet ditches; to give a platform for works or roads in marsh orheavy sand, &c. Thus, at the great battle of Blenheim, fascines were used by the Allies to enable them to cross the marshy rivulets which ran in front of the French position. And, in the attack of Acre by Buonaparte, in 1799, "the grenadiers moved forward from the trenches, but were stopped very soon by a wide and deep ditch with a revetted counterscarp. This obstacle, however, was soon surmounted. Fascines were thrown into the ditch, the ladders placed on them, and the troops descending, moved forward to assault," &c. ‡ For a similar purpose, Marlborough, when marching to surprise Villeroy's lines between the Meuse and Antwerp, made each trooper carry a truss of hay at his saddle-bow.-(Alison's Marlborough, p. 124.)

3d, Hurdles were much used by the ancients in their fieldworks, and are still occasionally found serviceable for revetting, or for laying on wet ground alternately with beds of fascines. Layers of hurdles, covered with heath and ballast, were exten* Fig. 43. Figs. 46, 47, 48, 49, 50. Article on Acre, in R. E. Papers, vol. vi. 28.

sively used by Stephenson in the sub-structure of the Liverpool and Manchester Railway, where it crosses Chat Moss. In the trenches at Antwerp, deluged with incessant rain, the French laid double tiers of fascines, and over these a layer of strong hurdles, for the passage of artillery.-(U. S. Journal for 1833, p. 360.)

Hurdles for portability may be made 6' long by 2′ 9′′ broad. Such a hurdle weighs about 50 pounds when dry.

Revetments may be made in hurdle-work, by driving stout stakes along the face of the slope to be revetted, to a depth of about 2 feet in the ground at its base. Branches are then woven in and out between these stakes, and vertical binders applied when the wattling is completed. Similar wattlework is employed in Flanders for revetting the submerged escarps of wet ditches.

4th, Sandbags are made of canvass, in the British service, usually 2′ 8′′ long by 1' 3" wide. They are most useful as a portable material, with which to construct a parapet or traverse in ground where excavation is difficult or undesirable; for the construction of loopholes on the top of a parapet;* for tamping or packing mines after they are charged; and for revetments in soil so loose that it would run through wickerwork.† If used, however, to line an embrasure or barbette, raw hides should cover the sand - bags, as they will be very apt to take fire from the discharge of the guns. Even fascines and gabions are liable to this accident in a dry climate. At Mooltan, in 1849, an experimental battery was formed by building up the solid portion entirely of fascines 9' long. Four officers of engineers and two Sepoy sappers erected a two-gun portion in little more than half-anhour, the material being close at hand. But the day after it was armed, the battery caught fire from the explosion of a shell from the citadel, and was entirely consumed.‡ At the British attack on the Havanna, in 1762, a fire broke out among the dry fascines and gabions, with which the besiegers' + Figs. 51, 52.

* Fig. 52.

The late Major Siddons's Journal of the Siege, in the R. E. Corps Papers, vol. i. 437.

works were formed, and continued to burn for two days, till the whole of the parapets were destroyed.

A filled sand-bag of the dimensions given is about 6′′ thick when built into a parapet, and weighs about 60 lb.

Besides the materials we have described, there are others used in the revetments of field-works. Woolpacks seem to have been a regular article of field equipment for forming lodgments, in the Continental wars during the time of Louis XIV. They were used abundantly in the attack of Edinburgh Castle, when held by the Duke of Gordon, after the Revolution in 1688.* And at the attack of Fort Christoval, opposite Badajos, in June 1811, woolpacks were employed to form the parapet of a battery on hard rock. This parapet was found throughout the siege to resist the shot, (at 450 yards from the place,) and preserve its shape remarkably well.† At Bhurtpoor, in 1825, parapets of cotton bales were found, at 800 or 900 yards from the fort, to resist every species of ordnance discharged against them—even an English 18 lb. shot, though the ball penetrated and rolled out harmless on the other side. But in the more advanced trenches, they proved of very little value. ‡

Sods, cut of a regular oblong form, built up in alternate layers of headers and stretchers, like bricks in a wall, make the best-looking, and probably the best of all revetments. Sods should be laid perpendicularly to the face of the slope, with the grass downwards. That the turf may bind well in with the earth of the parapet, both parts of the work should advance together. The interior slope of parapets should be revetted from the natural ground upwards, not from the newly-raised earth of the banquette.

If

In a dry climate, an excellent revetment may be made of earth wetted as for brick-making; or the whole parapet may be so constructed as in the celebrated mud-forts of India. time serves, for the higher class of field-works, pisé may be used-i. e., earth built up in successive masses, which are rammed hard in movable frames of strong plank, till a

* Grant's Memorials of Edinburgh Castle. + Jones's Sieges, i. p. 49.

Captain Boileau's Journal of the Siege.

consistency is attained, incredible to those who have not witnessed it.* In Upper India, and many other hot countries, fragments of the mouldering mud-walls, which abound, afford a ready and good material for revetments.

For escarps in loose soil it is usual to describe elaborate revetments of carpentry. But such work, on a great scale, is unsuitable to the circumstances of field-fortification, and its use must be very rare. If wood is abundant, it will be best applied in forming a detached escarp, such as that described by Sir J. Jones in a passage quoted above, (p.25.)

ACCESSARIES.

A few other accessaries of fortification in general remain to be described.

Traverses are detached lengths of parapet, constructed within a work,

1st, To bar the effects of enfilade fire.

2d, To diminish the destructive effect of bursting shells by intercepting their splinters.

3d, To screen the interior of the defences from a commanding eminence.

Or, 4th, To masque an opening left in a parapet for communication with the exterior.

Where the traverse is intended merely to intercept splinters, the face to which it is attached not being liable to enfilade, it need only be made of splinter-proof thickness, or from 2' to 5' at top. Such a traverse may readily be constructed of sandbags, or of a double tier of gabions. Its length will be 18 or 20 feet, sufficient to cover the gunners and guns in battery. It will be made of the same height as the parapet, and may be either attached to it, or separated from it by a space sufficient for communication.

Traverses on lines liable to enfilade should of course be shot-proof. It is usual to construct them between every two

* The walls of Moorish fortifications in Spain, such as the Alhambra and the castle at Gibraltar, appear to be composed of a sort of pisé of clay and gravel.-Murphy's Mahomedan Empire in Spain, 287. R. E. Papers, vol. iii. p. 92. Figs. 45 and 48.

or three

guns, on the faces of permanent works, as soon as a siege is apprehended. 12 feet at top is a usual thickness for such traverses.

The height of a traverse intended to screen the interior of a work will depend on the relative height and position of the ground from which the work is to be defiladed.

A traverse to mask an opening in a parapet is usually made inside, and parallel to the direction of the parapet. It should be long enough entirely to hide the interior from direct or oblique observation through the passage; and, being liable to be battered by the same metal as the parapet, it should be of the same thickness. A traverse adapted to these conditions will in small works be found to occupy a most inconvenient amount of room. Where the entrance to a field-work can be conveniently covered by being placed in a re-entering angle, or by one part of the parapet overlapping the other, (as in the field-work, fig. 63,) this is to be preferred.*

Musket and splinter-proof traverses might be compactly constructed of a single row of large gabions, like sap-rollers; of deal boxes filled with earth; or of masses of pisé.

Traverses for defilade, though perhaps occupying an inconvenient amount of interior space, may often prove of good service in prolonging the defence of a field-work. At the siege of Toulon, the British garrison of the fort called Little Gibraltar, by their obstinate defence of the interior traverses, caused great loss to the assailants, and long prevented their mastering the work. †

Traverses may also be turned to account, by forming them with hollow cells, or galleries lined with timber, to serve as magazines for ammunition. And the larger traverses have sometimes afforded space within their mass for the construction of splinter-proof accommodation for the repose of a part of the garrison.

A magazine may readily be obtained in the space formed by pieces of stout timber leaning at an angle against a wall or the interior slope of a parapet, and having the sloping surface covered with a foot or two of earth. Where timber is Dufour, Mémorial pour les Travaux de Guerre.

* Plate IV.