361 



BRIDGE HEAD. 



BRIDGES. 



303 



BRIDGE HEAD, or Tile de Pont, is a fortification covering that 

 extremity of a bridge which ia nearest to the position occupied by the 

 enemy, in order, by securing the line of communication, to facilitate 

 the advance of an army or protect its retreat. 



When a bridge is built across a river which runs through or along 

 one side of a fortified town, the ramparts of the town in the one case, 

 and those constructed for the defence of any buildings beyond the river 

 in the other, may be considered as constituting the bridge-head ; and 

 then the works enter into the class of permanent fortifications. In 

 other circumstances their form depends upon the nature of the ground, 

 and upon the importance of the pass to be secured. If a retreating 

 army is likely to be exposed to a serious attack when about to cross a 

 river, the works must be strong enough to keep the enemy in check, 

 and sufficiently extensive to contain the whole army, till the passage 

 can be effected. 



The simplest kind of bridge-head is one which has the form of a 

 redan ; that is, a breast-work, with two branches disposed on the plan 

 like the sides of the letter A, and terminating on the bank of the river. 

 But when a more perfect defence is required, the bridge-head may have 

 the figure of a horn-work, or of a bastioned front ; the area to be occu- 

 pied by the defenders being inclosed, except at the gorge or river side, 

 by the rampart or breast-work. When, however, the bridge-head is to 

 be sufficiently capacious to serve as an iutrenchment for the whole of an 

 army, it may consist of a series of redoubts or redans flanking each other 

 reciprocally, and disposed on a curve line whose extremities rest on the 

 river ; and whatever be the nature of the work, when its capacity is 

 considerable, it is always advisable to have a redan or small fort 

 immediately covering the bridge, acting as an interior retrenchment, 

 with its faces so disposed that their fire may defend the intervals 

 between, and flank the exterior redoubts. This retrenchment serves, 

 after the main body of the army has passed over the river, for a small 

 division acting as a rear-guard, to protect the retreat of the troops 

 employed in defending the principal works. The passages by which an 

 army or detachment, in retreating, enters a bridge-head consisting of a 

 continuous parapet, should be situated in the re-entering angles of the 

 work, if such there be, where they may be well flanked by crossing fires 

 from the collateral faces ; and they should be defended by a direct fire 

 from traverses in the interior. 



To prevent the enemy from advancing towards a bridge along the 

 b*tik on which the works are situated, that. lank, both on the right and 

 left of the bridge, should T>e well defended by a fire of musketry or 

 artillery ; consequently the parapets adjacent to the river should be as 

 near as possible perpendicular to its direction. And it is evident that 

 the most favourable situation for a military bridge is at a bend of 

 the river where the concavity is towards the enemy's position, for 

 the fortifications will thus conceal the bridge from his view ; and on 

 either side of the work the brisures intended to defend the ground 

 immediately in front may be directed towards the river, by which they 

 will be secure from an enfilading fire of the enemy. 



Should any commanding ground permit the enemy to direct a 

 plung ing fire of artillery upon the bridge or within the works, and 



should it be found impossible to give to the parapets a height 

 sufficiently great to intercept that fire, batteries or redoubts must be 

 constructed in convenient situations on the rear side of the river, in 

 order by their fire to prevent the enemy from occupying that ground. 

 Those works will also serve to defend the faces of the bridge-head 

 when attacked ; a traverse also should be raised on the same side of the 

 river, perpendicularly to the length of the bridge, in order to enfilade 

 the latter in the event of the enemy attempting to force a passage over 

 it before it can be destroyed. 



When there are island* in the river, it is advisable to establish the 

 bridges so that they may connect the islands with the opposite banks, 

 for thus ,the bridges, being shorter than if they were to extend quite 

 across the river, may be more numerous, consequently the passage of 

 the river will be facilitated and more effectually defended. There 

 should be a separate bridge-head for each bridge, besides the general 

 bridge-head on the farther bank ; and any collateral islands there may 

 be should be fortified, both to prevent the enemy from occupying 

 them, and thus obtaining a view of the bridge, and to afford the means 

 of flanking the principal bridge-head. 



The most important bridge-heads in Europe are on the Rhine, at 

 Ehrenbreitstein, Mannheim, Kehl, and Huninguen ; all these have been 

 celebrated in the wars of which the frontiers between France arid Ger- 

 many have so frequently been the theatre. 



BRIDGE, MILITARY. Military bridges may be classed under the 

 following heads : Pontoons ; Boat ; Rope ; Boat and Rope ; Cask ; 

 Trestle ; Raft ; Pile and Spar ; Flying Pivot ; Hying Trail. 



Pontoon and cask bridges are described under PONTOON ; flying pivot 

 and flying trail bridges, which are in fact nothing more than ferries, 

 under FLYING BRIDGE. 



Boat bridges are formed by an army, when unprovided with pon- 

 toons, from any small craft which can be collected on the river to be 

 crossed ; and when a bridge of this kind has to be formed in presence 

 of an enemy, feints should be made at various points of the river, to 

 deceive him as to the real place where, by a rapid movement, all the 

 accessible boats are collected. Decked boats, as used for cargo, are the 

 most adapted for the purpose ; and in order to make good the irre- 

 gularities in the heights of the various kinds, trestles are placed along 

 then- centres to carry the superstructure, the baulks of which should 

 never rest on the gunwales. The bridge constructed over the Indus by 

 Capt. G. Thomson, H. E. I. C. Engineers, which is described at page 92, 

 vol. iv. ' R. E. Corps' Papers,' is an excellent example of boat bridges, 

 for which no particular size and construction can be given, as they vary 

 so much with circumstances and the materiel procurable. 



Rope bridges are principally applicable -for spanning the broken arch 

 of a bridge, or for crossing a narrow river with steep banks. That con- 

 structed by Col. Sturgeon over the broken arch at Alcantara (in 1810), 

 which spanned 100 feet, is an example both of method of construction 

 and applicability of this material, where, as in this case, timber cannot 

 be procured, or great portability is desired. Boat and rope bridges are 

 often of great use. The bridge over the Adour, designed by Col. Stur- 

 geon and executed by the Royal Engineers, is perhaps the best example 

 ever constructed. The method of stretching the rope- work was much 

 the same as that used at Alcantara, and will be found described in Sir 

 H. Douglas's work on military bridges. The boats used were 48 

 chatte-mnriei, which were anchored stem and stern, to meet the run of 

 the tide both ways, at first with one, but afterwards with two anchors, 

 on account of the violence of the current. Trestle bridges are chiefly 

 applicable to streams in mountainous countries, liable to sudden rises, 

 and therefore often unfordable; and where the previously mentioned 

 means are not procurable. The trestles are made of any rough timber, 

 sufficiently high to carry the superstructure above any probable rising of 

 the water, and are kept firm by being loaded with stones at the bottom, 

 and by strong ropes or cables passed across and fastened to the tops. 

 Sir H. Douglas mentions a trestle bridge constructed across the Agueda 

 by Col. Sturgeon, which was 396 feet long, and carried on eighteen 

 trestles. 



Raft bridges are ill adapted to an army, as they are very* unmanage- 

 able, especially when the passage is contested, and besides having 

 little buoyancy, become waterlogged when kept long in the water. 

 They have the advantage, however, where timber is plentiful along 

 the bank of a river, of being made on the spot and requiring few 

 skilled workmen, a few cables being the only materiel brought from 

 the rear. 



Pile and spar bridges are a more permanent description of bridge, 

 though occasionally, when the stream is wide and deep, and the bottom 

 suitable for pile-driving, they may be of great service to the military 

 engineer. 



For further particulars on this most important subject in military 

 science, the student is referred to Sir Howard Douglas on Military 

 Bridges, and the R. E. ' Aide Mdmoire,' from which the above has prin- 

 cipally been taken. 



BRIDGES are of two classes, public and private. Public bridges 

 may be considered either as county bridges or as highways, although 

 the principle of that distinction does not seem very clear. Every 

 county bridge is a highway, inasmuch as it is a bridge over which a 

 highway passes ; it is therefore in that respect strictly a highway : so 

 also is every other public bridge over which a highway passes. The 

 usual distinction drawn between them is derived from the nature of 



