FORTIFICATION AND SIEGECRAFT. "Fortifica tion" is the military art of strengthening positions against attack. The word (Lat. fortis, strong, and facere, to make) implies the creation of defences. Thus the boy who from the top of a mound defies his comrades, or shelters from their snowballs behind a fence, is merely taking advantage of ground; but if he puts up a hurdle on his mound and stands behind that he has fortified his position.
Fortification has two tactical objects—to obtain the fullest advantage from one's own weapons; and to prevent the enemy using his to advantage. It consists of two elements, viz., protection and obstacle. The protection shields the defender from the enemy's missiles; the obstacle prevents the enemy from coming to close quarters, and delays him under fire.
Protection may be of several kinds, direct or indirect. Direct protection is given by a wall or rampart of earth, strong enough to stop the enemy's missiles. The value of this is reduced in pro portion as the defender has to expose himself to return the enemy's fire, or to resist his attempts to destroy the defences. Indirect protection is given by distance, as for instance by a high wall placed on a cliff so that the defender on the top of the wall is out of reach of the enemy's missiles if these are of short range, such as arrows. This kind of defence has naturally lost much of the value that it had in earlier times. Another form of indirect protection of great importance is concealment.
The obstacle may consist of anything which will impede the enemy's advance and prevent him from coming to close quarters. In the earliest forms of fortification the protecting wall was also the obstacle, or it may be a wet or dry ditch, an entanglement, a swamp, a thorn hedge, a spiked palisade, or some temporary ex pedient, such as chevaux de frise. The two elements must of course be arranged in combination. The besieged must be able to defend the obstacle from their protected position, otherwise it can be surmounted or destroyed at leisure.
Protection must be arranged mainly with reference to the enemy's methods of attack and the weapons he uses. The obstacle, on the other hand, should be of such a nature as to bring out the best effects of the defender's weapons. It follows from this that a well-armed force operating against a badly-armed, uncivilized enemy may use with advantage very simple old-fashioned methods of protection ; or even dispense with it altogether if the obstacle is a good one. When the assailant has modern weapons the im portance of concealment and protection is very great. In fact, it may be said that in proportion as missile weapons have grown more effective, the importance of protection and the difficulty of providing it have increased, while the necessity for a monumental physical obstacle has decreased. The art of the engineer who is about to fortify consists in appreciating and harmonizing all the conditions of the problem, such as the weapons in use, nature of the ground, materials available, temper of assailants and defend ers, strategical possibilities, expenditure to be incurred, and so forth. The keynote of the solution should be simplicity; but this is the first point usually lost sight of by the makers of "systems," especially by those who during a long period of peace have time to give play to their imaginations.
Fortification is usually divided into two branches, namely permanent fortification and field fortification. Permanent forti fications are erected at leisure, with all the resources that a state can supply of constructive and mechanical skill, and are built of enduring materials. Field fortifications are extemporized by troops in the field, perhaps assisted by such local labour and tools as may be procurable, and with materials that do not require much preparation, such as earth, brushwood and light timber. In the course of a campaign these may, as in the World War, be developed into semi-permanent fortification.
The objects of fortification are various. The vast enceintes of Nineveh and Babylon were planned so that in time of war they might give shelter to the whole population of the country except the field army, with their flocks and herds and household stuff. In the middle ages, feudal lords built castles for security against the attacks of their neighbours, and also to watch over towns or bridges or fords from which they drew revenue ; whilst rich towns were surrounded with walls merely for the protection of their own inhabitants and their property. The feudal castles lost their importance when the art of cannon-founding was fairly developed; and in the leisurely wars of the 17th and 18th centuries, when roads were few and bad, a swarm of fortified towns, large and small, played a great part in delaying the march of victorious armies. In the present day isolated forts are seldom used, and only for such purposes as to block passes in mountainous districts. Fortified zones are used either to protect points of vital impor tance, such as capital cities, military depots and dockyards, or at strategic points such as railway junctions. Fortified areas are also used for more general strategic purposes, as will be explained later.
The most elementary type of fortification is the thorn hedge, a type which naturally recurs from age to age under primitive conditions. Thus, Alexander found the villages of the Hyrcanians defended by thick hedges, and the same arrangements have been seen in recent times among the least civilized tribes of Africa. The next advance from the hedge is the bank of earth. with the exte rior made steep by revetments of sods or hurdle-work. This has a double advantage over the hedge, as, besides being a better obstacle against assault, it gives the defenders an advantage of position in a hand-to-hand fight. Such banks formed the defences of the German towns in Caesar's time, and they were constructed with a high degree of skill. Timber being plentiful, the parapets were built of alternate layers of stones, earth and tree trunks. The latter were built in at right angles to the length of the parapet, and were thus very difficult to displace, while the earth prevented their being set on fire. The bank was often strengthened by a palisade of tree trunks or hurdle-work.
After the bank the most important step in advance for a nation progressing in the arts was the wall, of masonry, sun-dried brick or mud. The history of the development of the wall and of the methods of attacking it is the history of fortification for several thousand years. The first necessity for the wall was height, to give security against escalade. The second was thickness, so that the defenders might have a platform on the top which would give them space to circulate freely and to use their weapons. A lofty wall, thick enough at the top for purposes of defence, would be very expensive if built of solid masonry; therefore, the plan was early introduced of building two walls with a filling of earth or rubble between them. The face of the outer wall would be carried up a few feet above the platform, and crenellated to give protec tion against arrows and other projectiles. The next forward step for the defence was the construction of towers at intervals along the wall. These provided flanking fire along the front ; they also afforded refuges for the garrison in case of a successful escalade, and from them the platform could be enfiladed. The evolution of the wall with towers was simple. The main requirements were despotic power and unlimited labour. Thus the finest examples of the system known to history are also amongst the earliest. One of these was Nineveh, built more than 2,000 years B.C. The object of its huge perimeter, more than 5om., has been mentioned. The wall was i2oft. high and Soft. thick; and there were 1,50o towers. After this no practical advance in the art of fortification was made for a very long time, from a constructional point of view. Many centuries, indeed, elapsed before the inventive genius of man evolved engines and methods of attack fit to cope with such colossal obstacles.
The earliest form of attack was, of course, escalade, either by ladders or by heaping up a ramp of faggots or other portable materials. When the increasing height of walls made escalade too difficult, other means of attack had to be invented. Probably the first of these were the ram, for battering down the walls, and mining. The latter might have two objects : (a) to drive an under ground gallery below the wall from the besiegers' position into the fortress, or (b) to destroy the wall itself by undermining. The use of missile engines for throwing heavy projectiles probably came later. They are mentioned in the preparations made for the defence of Jerusalem against the Philistines in the 8th century B.C. They are not mentioned in connection with the siege of Troy. At the sieges of Tyre and Jerusalem by Nebuchadrezzar in 587 B.C., we first find mention of the ram and of movable towers placed on mounds to overlook the walls.
In fortification the wall with towers was still the leading idea. The towers were preferred circular in, plan, as this form offered the best resistance to the ram. The wall was usually reinforced by a ditch, which had three advantages: it increased the height of the obstacle, made the bringing up of the engines of attack more dif ficult, and supplied material for the filling of the wall. In special cases, as at Jerusalem and Rhodes, the enclosure walls were doubled and trebled. Citadels were also built on a large scale. The typical site preferred by the Romans for a fortified town was on high ground sloping to a river on one side and with steep slopes falling away on the other three sides. At the highest point was a castle serving as a citadel. The town enclosure was designed in accordance with the character of the surrounding country. Where the enemy's approach was easiest, the walls were higher, flanking towers stronger and ditches wider and deeper. Some of the towers were made high for look-out posts. If there was a bridge over the river, it was defended by a bridge-head on the far side; and stockades defended by towers were built out from either bank above and below the bridge. between which chains or booms could be stretched to bar the passage. The natural features of the ground were skilfully utilized. Thus when a large town was spread over an irregular site broken by hills, the enceinte wall would be carried over the top of the hills ; and in the intervening valleys the wall would not only be made stronger, but would be somewhat drawn back to allow of a flanking defence from the hill tops on either side. The walls would consist of two strong masonry faces, 20 f t. apart, the space between filled with earth and stones. Usu ally when the lie of the ground was favourable, the outside of the wall would be much higher than the inside, the parapet walk perhaps being but a little above the level of the town. Palisades were used to strengthen the ditches, especially before the gates.
There was little scope, however, in masonry for the genius of Roman warfare, which had a better opportunity in the active work of attack and defence. For siegecraft the Roman legions were especially apt. No modern engineer, civil or military, accustomed to rely on machinery, steam and hydraulic apparatus, could hope to emulate the feats of the legionaries. In earthworks they ex celled ; and in such work as building and moving about colossal wooden towers under war conditions, they accomplished things at which nowadays we can only wonder. The attack was carried on mainly by the use of "engines," under which head were included all mechanical means of attack—towers, missile engines such as catapults and balistae, rams of different kinds, "tortoises" (see below), etc. Mining, too, was freely resorted to, also approach trenches, the use of which had been introduced by the Greeks. The object of mining, as has been said, might be the driving of a gallery under the wall into the interior of the place, or the destruc tion of the wall. The latter was effected by excavating large cham bers under the foundations. These were supported while the exca vation was proceeding by timber struts and planking. When the chambers were large enough the timber supports were burnt, and the wall collapsed. The besieged replied to the mining attack by counter-mines. With these they would undermine and destroy the besiegers' galleries, or would break into them and drive out the workers, either by force of arms or by filling the galleries with smoke.
Breaches in the wall were made by rams. These were of two kinds. For dislodging the cemented masonry of the face of the wall, steel-pointed heads were used; when this was done, another head, shaped like a ram's head, was substituted for battering down the filling of the wall. For escalade they used ladders fixed on wheeled platforms ; but the most important means of attack against a high wall were the movable towers of wood. These were built so high that from their tops the parapet walk of the wall could be swept with arrows and stones; and drawbridges were let down from them by which a storming party could reach the top of the wall. The height of the towers was from 7o to 'Soft. They were moved on wheels of solid oak or elm, six to ' 2ft. in diameter and three to four feet thick. The ground floor contained one or two rams. The upper floors, of which there might be as many as 15, were furnished with missile engines of a smaller kind. The archers occupied the top floor. There also were placed reservoirs of water to extinguish fire. These were filled by force pumps and fitted with hose made of the intestines of cattle. Drawbridges, either hanging or worked on rollers, were placed at the proper height to give access to the top of the wall, or to a breach, as might be required. Apollodorus proposed to place a couple of rams in the upper part of the tower to destroy the crenellations of the wall. The siege towers had of course to be very solidly built of strong timbers to resist the heavy stones thrown by the engines of the defence. They were protected against fire by screens of osiers, plaited rope or raw hides. Sometimes it was necessary, in order to gain greater height, to place them on high terraces of earth. In that case they would be built on the site. At the siege of Marseille, described by Caesar, special methods of attack had to be employed on account of the strength of the engines used by the besieged and their frequent sallies to destroy the siege works. A square fort, with brick walls Soft. long and 5ft. thick, was built in front of one of the towers of the town to resist sorties. This fort was subsequently raised to a height of six storeys, under shelter of a roof which projected beyond the walls, and from the eaves of which hung heavy mats made of ships' cables.
The mats protected the men working at the walls, and as these were built up the roof was gradually raised by the use of endless screws. The roof was made of heavy beams and planks, over which were laid bricks and clay, and the whole was covered with mats and hides to prevent the bricks from being dislodged. This struc ture was completed without the loss of a man, and could only have been built by the Romans, whose soldiers were all skilled workmen. Although these towers were provided with bridges by which storming parties could reach the top of the wall, their main object was usually to dominate the defence and keep down the fire from the walls and towers. Under this protection breaching operations could be carried on. The approaches to the wall were usually made under shelter of galleries of timber or hurdle-work, which were placed on wheels and moved into position as required. When the wall was reached, a shelter of stronger construction, known as a "rat," was placed in position against it. Under this a ram was swung or worked on rollers ; or the rat might be used as a shelter for miners or for workmen cutting away the face of the wall. The great rat at Marseille, which extended from the tower already described to the base of the tower of the city, was 6oft. long, and built largely of great beams two feet square, connected by iron pins and bands. It was unusually narrow, the ground sills of the side walls being only four feet apart. This was no doubt in order to keep down the weight of the structure, which, massive as it was, had to be movable. The sloping roof and sides of timber were protected, like those of the tower, with bricks and moist clay, hides and wool mattresses. Huge stones and barrels of blazing pitch were thrown from the wall upon this rat without effect, and under its cover the soldiers loosened and removed the foundations of the tower until it fell down. In order that it might be possible to move these heavy structures, it was usually necessary to fill up the ditch or to level the surface of the ground. For this purpose, an "approach tortoise" was often used. This was a shelter, something between the ordinary gallery and the rat, which was moved end on towards the wall, and had an open front with a hood, under cover of which the earth brought up for filling the ditch was distributed.
The missile engines threw stones from 75 lb. up to 600 lb. weight, heavy darts from six to i 2f t. long, and Greek fire. Archimedes at the siege of Syracuse even made some throwing i,800 lb. The ranges varied, according to the machine and the weight thrown, up to 600yd. for direct fire and i,000yd. for curved fire. In addition to the above, great mechanical skill was shown in the construction of special varieties of machines. A kind of jib crane of great height on a movable platform was used to hoist a cage containing 15 or 20 men on to the wall. A long spar with a steel claw at the end, swung in the middle from a lofty frame, served to pull down the upper parts of parapets and overhanging galleries. The defenders on their side were not slow in replying with similar devices. Fenders were let down from the wall to soften the blow of the ram, or the ram heads were caught and held by cranes. Grapnels were lowered from cranes to seize the rats and overturn them. Archimedes used the same idea in the defence of Syracuse for lifting and sinking the Roman galleys. Wooden towers were built on the walls to overtop the towers of the besiegers. Many devices for throwing fire were employed. The tradition that Archimedes burnt the Roman fleet. or a portion of it, at Syracuse, by focusing the rays of the sun with reflectors, is supported by an experiment made by Buffon in 1747. With a reflector having a surface of 5osq.f t., made up of 168 small mirrors each six by eight inches, lead was melted at a distance of i 4of t. and wood was set on fire at 16o feet. The development of masonry in permanent fortification had long since reached its practical limit, and the attack had become stronger than the defence.
. . . The external ground-level was much lower than that of the tower. . . . T h e battlemented portion at the top was covered with a roof, and open on the side of the town in order to permit the defenders of the tower to see what was going on therein, and also to allow of their hoisting up stones and other projectiles by means of a rope or pulley." (See fig. I.) Meanwhile, in western Europe, siegecraft had almost disap peared. Its perfect development was only possible for an army like that of the Romans. The Huns and Goths knew nothing of it, and the efforts of the Frankish kings to restore the art were hampered by the fact that their warriors despised handicrafts and understood nothing but the use of their weapons. During the dark ages the towns of the Gauls retained their old Roman and Visigoth defences, which no one knew properly how to attack, and which rarely fell except through blockade and famine. It was not until the i r th century that siegecraft was revived in the West, and by this time the seigneurial castle (q.v.), had come into existence. Built primarily as strongholds for local magnates or for small bodies of warriors dominating a conquered country, these had special defensive assets, whereas the defences of a town had to follow the growth of the town, and would naturally have weak points. The site of a castle could be chosen purely for its natural strength ; and as its area was small it was often easy to find a natural position entirely suited for the purpose. A small hill with steep sides might well be unapproachable by such cum brous structures as towers and rats, while the height of the hill, added to the height of the walls, would be too much for the besiegers' missiles. If the sides of the hill were precipitous and rocky, mining became impossible, and the site was perfect for defence. A castle built under such con ditions was practically impregnable ; and this was the cause of the independence of the barons in the i i th and 12th centuries.
They could only be reduced by blockade, and a blockade of long duration was very difficult in the feudal age.
A very instructive example of i 2th century work is the Chateau Gaillard, built by Richard Coeur-de-Lion in 1196.
In the article CASTLE will be found the plan of the main work, which is here supplemented by an elevation of the don jon (or keep) . The waved face of the inner or main wall of the castle, giving a divergent fire over the front, is an inter esting feature in advance of the time. After the death of Richard, Philip Augustus be sieged the chateau, and carried it after a blockade of seven months and a regular attack of one month. In this attack the tower at A was first mined, after which the whole of that outwork was aban doned by the defenders. The outer enceinte was next captured by surprise ; and finally the gate of the main wall was breached by the pioneers. When this happened a sudden rush of the besiegers prevented the remains of the garrison from gaining the shelter of the donjon, and they had to lay down their arms. Chateau Gaillard, designed by pefhaps the greatest general of his time, exemplifies in its brief resistance the weak points of the designs of the i 2th century. At each step gained by the besiegers the very difficulties which had been placed in the way of their further advance prevented the garrison from reinforcing strongly the points attacked.
In the 13th century many influences were at work in the de velopment of castellar fortification. The experience of such sieges as that of Chateau Gaillard, and still more that gained in the Crusades, the larger garrisons at the disposal of the great feudal lords, and the importance of the interests which they had to pro tect in their towns, led to a freer style of design. We must also take note of an essential difference between the forms of attack preferred by the Roman soldiery and by the mediaeval chivalry. The former, who were artisans as well as soldiers, preferred in siege works the certain if laborious methods of breaching and mining. The latter, who considered all manual labour beneath them and whose ideal of warfare was personal combat, affected the tower and its bridge, giving access to the top of the wall rather than the rat and battering ram. We find, therefore, important progress in enlarging the area of defence and in improving ar rangements for flanking. The size and height of all works were increased. The keep of Coucy castle, built in 1220, was goof t. high. Montargis castle, also built about this time, had a central donjon and a large open enclosure, within which the whole gar rison could move freely, to reinforce quickly any threatened point. The effect of flanking fire was increased by giving more projection to the towers, whose sides were in some cases made at right angles to the curtain walls. We find also a tendency towards complexity and multiplication of defences, to guard against sur prise and localize successful assaults. Great attention was paid to the "step by step" defence. Complicated entrances with traps and many doors were arranged. Almost all defence was from the tops of the wall's and towers, Machicouli galleries being employed for vertical defence.
The defences of Carcassonne, remodelled in the latter half of the i3th century, exemplify some of the best work of the period. There are only two gates. That on the east is defended by two great towers and a semicircular barbican. The gate of the castle, on the west, has a most complicated approach, and beyond this is a huge circular barbican in several storeys. On the side of the town the castle is protected by a wide moat, and the entrance is masked by another large semicircular barbican. An interesting feature is the importance which the lists have assumed. The slight wooden barricade of older times has developed into a wall with towers ; and the effect is that the besieger, if he gains a footing in the lists, has a very narrow space in which to work the engines of attack. The castle, after the Roman fashion, adjoins the outer wall of the town, so that there may be a possibility of communi cating with a relieving force from outside after the town has fallen. There were also several posterns, small openings made in the wall at some height above the ground, for use with rope ladders. The siegecraft of the period was still that of the ancients. Min ing was the most effective form of attack, and the approach to the walls was covered by engines throwing great stones against the hoardings of the parapets, and by cross-bowmen who were shel tered behind light mantlets moved on wheels. Barrels of burning pitch and other incendiary projectiles were thrown as before; and at one siege we read of the carcasses of dead horses and bar rels of sewage being thrown into the town to breed pestilence, which had the effect of forcing a capitulation. With all this the attack was inferior to the defence, owing to the inherent limita tions of the "engineer," until gunpowder was introduced.
Before beginning to trace the effect of gunpowder on the de sign of fortification, it may be noted that two causes weakened the influence of the castles. First, their owners were slow to adopt the new ideas and abandon their high strong walls for low ex tended parapets, and, secondly, they had not the men necessary for long lines of defence. At the same time the corporations of the towns had learnt to take an active part in warfare, and pro vided trained and disciplined soldiers in large numbers. When artillery became strong enough to destroy masonry from a dis tance two results followed : it was necessary to modify the ma sonry defences so as to make them less vulnerable, and to im prove the means of employing the guns of the defence. For both these purposes the older castles with their restricted area were little suited, and we must now trace the development of the fortified towns. Probably the first form of construction directly due to the appearance of the new weapons was the bulwark ( boulevard, baluardo or bollwerk) . This was an outwork usually semicircular in plan, built of earth consolidated with timber and revetted with hurdles. Such works were placed as a shield in front of the gates, and they offered at the same time advanced positions for the guns of the defence. The first real lesson taught by improved artillery was that the walls should not be set up on high as targets, but in some manner screened ; in the case of old works, by placing bulwarks in front of them ; in new works by sinking the wall in a ditch.
For resistance to the effect of shot the most valuable expedient was the use of counterforts. The earliest counterforts were simply buttresses built inward from the wall into the rampart in stead of outward. The effect of these was to strengthen the wall and make the breaches more difficult of ascent. An al ternative arrangement for strengthening the wall was an arched gallery built behind it under the rampart. More important still was the development of the active defence by artillery. For this purpose it was necessary to find room for the working of the guns. Various modifications of the existing masonry defences were tried, but the natural solution, soon generally adopted, was the rampart ; that is, a bank of earth thrown up behind the wall, which while strengthening the wall as already indicated, offered plenty of space for the disposal of the guns.
The ditch, which had only been occasionally used in ancient and mediaeval fortification, now became essential and character istic. Serving as it did the double purpose of supplying earth for a rampart and allowing the wall to be sunk for concealment, it was found also to have a definite use as an obstacle. Hitherto the wall has sufficed for this purpose, the ditch being useful mainly to prevent the besieger from bringing up his engines of attack.
When the wall (or escarp) was lowered, the obstacle offered by the ditch was increased by revetting the far side of it with a counterscarp. Beyond it some of the earth excavated from the ditch was piled up to increase the protection given to the escarp wall, and sloped gently in such manner as to be swept by the fire from the ramparts; this was called the glacis. But the intro duction of the counterscarp wall pre vented sorties from the ditch, as hitherto, against the besiegers. Hence a space, at ground-level, came to be left behind the glacis, allowing room for troops to assemble. This was known as the covered way. With this last addition the ordinary elements of a profile of "post-gunpowder" fortification were complete.
Up to the gunpowder period the trace of fortifications, that is, the plan on which they were arranged on the ground, was very simple. It was merely a question of an enclosure wall adapted to the site and provided with towers at suitable intervals. The foot of the wall could be seen and defended everywhere, from the tops of the towers and the machicoulis galleries. The intro duction of ramparts and artillery made this more difficult. The rampart, interposed between the defenders and the face of the wall, put a stop to vertical defence, while guns from the top of the wall could not be depressed sufficiently for flanking fire along the ditch. The problem of the "trace," therefore, at the begin ning of the i6th century was to rearrange the line of defence so as to give due opportunity to the artillery of the besieged. At first for flanking purposes casemates on the ditch level were used, the old flanking towers being enlarged for the purpose. Some use was also made of the fire from detached bulwarks. It was soon real ized, however, that the flanking defence of the body of the place ought not to be dependent on outworks, and that greater freedom was required for guns than was consistent with casemate defence. The bulwark was too detached for security. The enlarged tower, as an integral part of the lines, gave security, and its walls at right angles to the curtain gave direct flanking fire, but the guns in it were too cramped. The blending of the two ideas produced the bastion, an element of fortification which dominated the science for 30o years. The word has been in use for a long time in con nection with extemporized towers or platforms for flanking pur poses, the earliest forms being bastille, bastide, bastillon, and in its origin it apparently refers rather to the quality of work in the construction than to its defensive intention. The earliest bastions were modified bulwarks with straight faces and flanks, attached to the main wall, for which the old towers often acted as keeps; and at first the terms bulwark and bastion were more or less interchangeable.
Towards the end of the 16th century the term "bulwark" began to be reserved for banks of earth thrown up a little distance in front of the main wall to protect it from breaching fire. "Bastion" henceforth denoted an artillery position connected by flanks to the main wall; and the question of the arrangement of these flanks was one of the main preoccupations of engineers. Thus, while in the early part of the i6th century the actual modification of existing defences was proceeding very slowly on account of the expense involved, the era of theoretical "systems' had begun, based on the mutual relations of flank and face. These can be grouped under three heads as follows : I. The cremaillere or indented trace: Faces and flanks succeeding each other in regular order (fig. 4) .
2. The tenaille trace: Flanks back to back between the faces (fig. 5) . The development of the flanks in this case gives us the star trace (fig. 6) .
3. The bastioned trace: Flanks facing each other and connected by curtains (fig. 7) .
In comparing these three traces it will be observed that unless casemates are used the flanking in the first two is incomplete. Guns on the ramparts of the faces cannot defend the flanks, and therefore there are "dead" angles in the ditch. In the bastioned trace there is no '`dead'" ground, provided the flanks are so far apart that a shot from the rampart of a flank can reach the ditch at the centre of the curtain. Here was therefore the parting of the ways. For those who objected to casemate tire, the bastioned trace was the way of salvation. They were soon in the majority; per haps because the symmetry and completeness of the idea capti vated the imagination. At all events the bastioned trace, once fairly developed. held the field in one form or another practically without a rival until near the end of the i 8th century. The Italian engineers, who were supreme throughout most of the t 6th century, started it; the French, who took the lead in the following century, developed it.
It will be useful at this print to go forward a little, with a simple explanatory figure, in order to get a grasp of the component parts of the bastioned trace as ultimately developed, and of its outworks.
(The line of the escarp is called the magistral line since it regulates the trace. When plans of fortifications are given without much detail, this line, with that of the counterscarp and the crest of the parapet, are often the only ones shown—the crest of the parapet, as being the most important line, whence the fire proceeds, being usually emphasized by a thick black line.) Fig. 8, reproduced from a French engraving of i 7o5, shows an imaginary place fortified as a hexagon with bastions and all the different kinds of outworks then in use. The following is the explana tion of its figuring and lettering: i. Flat bastion: Placed in the middle of a curtain when the lines of defence were too long for musketry range.
3. Tenaille bastion: Used when the flanked angle is too acute: that is, less than ;o°.
C. Demi-lunes: So called from the shape of the gorge. They differ from the ravelins in being placed in front of the bastions instead of the curtains.
D. Counter-guards: Used instead of demi-lunes, which were then going out of fashion.
E. Simple tenaille.
(If the tenaille E is reduced in width towards the gorge, as shown alternatively, it is called a swallow-tail. If the double tenaille is reduced as at G, it is called a bonnet de prctre. Such works were rarely used.) H. Hornwork : Much used for gates, etc.
I. Crown-work.
L. M. New forms of tenaille: (N.B.—These are the forms which ultimately retained the name) .
N. New form of work called a demi-tune lunettee, the ravelin N being protected by two counter-guards, 0.
Q. Traverses.
R. Salient places of arms.
&. Traverses to protect the terreplein of the ramparts from enfilade.
Turning back now to the middle of the 16th century we find in the early examples of the use of the bastion that there is no at tempt made to defend its faces by flanking fire, the curtains being considered the only weak points of the enceinte. Accordingly, the flanks are arranged at right angles to the curtain. and the prolonga tion of the faces sometimes falls near the middle of it. When it was found that the faces needed protection, the first attempts to give it were made by erecting cavaliers, or raised parapets, behind the parapet of the curtain or in the bastions. The first example of the complete bastioned system is found in Paciotto's citadel of Antwerp. built in 1568. In this case we have faces, flanks and curtain in due proportion; the faces long enough to contain a pow erful battery. and the flanks able to defend both curtain and The weak points of this trace. due to its being arranged on a small pentagon, are that the terreplein or interior space of the bastions is rather cramped, and the salient angles too acute.
In the systems published by Speckle of Strasbourg in 1589 we find a distinct advance—in the absence of outworks, the use of cavaliers and double parapets and in his own particular invention of the low batteries behind the re-entering place of arms and the gorge of the ravelin. But his ideas were rather in advance of the powers of the artillery of his day.
Early in the t ; th century Marchi and Busca in Italy, if exces sively geometrical, and de Ville and Pagan in France, contributed to the evolution of fortification. It is the latter half of the 17th century, however, which is one of the most important periods in the history of fortification, chiefly because it was illuminated by the work of Vauban. It was at this time also that a prodigious output of purely theoretical fortification began, which went on till the French Revolution. Many of the "systems" published at this time were elaborated by men who had no practical knowledge of the subject, and they tended to a multiplication of outworks which culminated in such extravagances as the system of Rhana, pub lished in 1769.
Vauban's "first system," as variously described by other writers even in his own time, is pieced together from some of the early examples of his work. The "second system" is the "tower bastion" defence of Belfort and Landau (1684-88) , obviously suggested by a design of Castriotto's ioo years earlier; and the "third system" is the front of Neu-Breisach (1698), which is merely Landau slightly improved. In other works, between 1688 and 1698, he did not keep to the tower bastion idea. It will be convenient to take the "first system," as reproduced in a text-book of fortification as typical of much of Vauban's best work. He sometimes uses the straight flank, and sometimes the curved flank with orillon. Parapets in several tiers are never used, nor cavaliers. The ravelin is almost always used. It is small, having little artillery power and giving no protection to the shoulders of the bastions. The tenaille is very generally found. In this form, viz., as a shield to the escarp of the curtain, it was probably invented by him. There were two forms. Traverses are used for the first time on the covered way to guard against enfilade fire ; and the re-entering place of arms, to which Vauban attached considerable importance, is large. The main dimensions of the trace are indicated. As regards the profile the bastions and curtain have a command of 2 5f t. over the country, i7ft. over the crest of the glacis and 8ft. over the rave lin. The ditches are i8ft. deep throughout. The parapets are i8ft. thick with full revetments. In his later works he used demirevetments.
After Vauban died, though the theories continued, the valuable additions to the systems were few. Among his successors Cormon taigne (q.v.) formed a link with the school of Mezieres, established in i 748, and from this time forward there was an official school of thought, based on Vauban. Cormontaigne's work, therefore, repre sents the modifications of Vauban's ideas accepted by French en gineers in the latter part of the i 8th century. The school of Mezieres was afterwards replaced by that of Metz, which carried on its traditions. Such schools are necessarily conservative, and hence, in spite of the gradual improvement in ordnance and fire arms, we find the main elements of the bastioned system remaining unchanged right up to the period of the Franco-German war in 187o. Chasseloup-Laubat tells us that, before the Revolution, to attempt novelties in fortification was to write one's self down ig norant. As, therefore, the official view was that the general out lines of the system were sacred, the efforts of orthodox engineers from Cormontaigne's time onwards were given to improvements of detail, and mainly to retard breaching operations as long as possible. Among the unorthodox two names deserve mention. The first of these is Chasseloup-Laubat (q.v.), who served throughout the wars of the Republic and Empire, and constructed the fortress of Alessandria in Piedmont. Chasseloup's main proposals to im prove the bastioned system were two : First, in order to prevent the bastions from being breached through the gaps made by the ditch of the ravelin, he threw forward the ravelin and its keep out side the main glacis. This had the further advantage of giving great saliency to the ravelin for cross-fire over the terrain of the attack. On the other hand, it made the ravelin liable to capture by the gorge, and thus was dangerous for a weak or inactive garrison. Secondly, in order to get freedom to use longer fronts than those admissible for the ordinary bastioned trace, he proposed to extend his exterior side up to about 65oyd. and to break the faces of his bastions; the portion next the shoulder being defended from the flank of the collateral bastion and coinciding with the line of de fence, and the portion next the salient, up to about Boyd. in length, being defended from a central keep or caponier placed in front of the tenaille. The natural criticism of this arrangement is that it combines some of the defects of both the bastioned and polygonal systems without getting the full advantages of either.
The second name is that of Capt. Choumara of the French En gineers, born in 1787, whose work was published in 1827. Two leading ideas were due to him. The first is that of the "inde pendence of parapets." By making the crest of the parapet quite independent of the escarp line he obtained great freedom of direc tion for his fire. The second idea is that of the "inner glacis." This was a glacis parapet placed in the main ditch to shield the escarp; its effect being to prevent the escarp of the body of the place from being breached in the usual way by batteries crowning the crest of the covered way. The need for Choumara's improvements has passed by, but he was in his time a real teacher. One sentence of his strikes a resounding note : "What is chiefly required in fortifi cation is simplicity and strength. It is not on a few little contriv ances carefully hidden that one can rely for a good defence. The fate of a place should not depend on the intelligence of a corporal shut up in a small post prepared for his detachment." It must here be remarked that the reproach of "geometrical" fortification is in no way applicable to the works of Vauban and his immediate successors. They excelled in adapting works to sites, the real test of the engineer. The bastioned system was the 17th century solution of the fortification problem. Given an artillery and musketry of short range and too slow for effective frontal de fence, a ditch is necessary as an obstacle. What is the best means of flanking the ditch and of protecting the flanking arrangements? If Vauban elected for the bastion, we must before criticizing his choice remember that he was the most experienced engineer of his day, a man of the first ability and quite without prejudice. What is matter for regret is that the authority of Vauban should have prac tically paralysed the French school during the i8th and most of the i9th century, so that while the conditions of attack and defence were gradually altering they could admit no change of idea, and their best men, who could not help being original, were struggling against the whole weight of official opposition. Again, the duplica tion of outworks often seen is not geometric fortification. It is a definite attempt to retard the attack, on ground favourable to it, by successive lines of defence.
Coehoorn (q.v.), the contemporary and nearest rival to Vau ban, was the greatest light of the Dutch School. Like Vauban he was distinguished as a fighting engineer, both in attack and de fence ; but in the attack he differed from him in relying more on powerful artillery fire than systematic earth-works. He intro duced the Coehoorn mortar.
Landsberg the younger (167o-1746), a major-general in the Prussian service, appears to have been the first who frankly advo cated the tenaille alone, chiefly on the ground that the flank, which was the most important part of the bastioned system, was also the weakest. It was, however, ultimately a Frenchman, Marc Rene Montalembert (q.v.), who was the great apostle of the tenaille, though in his later years he leaned more to the polygonal trace. He objected to the bastioned trace on many grounds; principally that the bastion was a shell trap, that the flanks by crossing their fire lost the advantage of the full range of their weapons, and that the curtain was useless for defence. His tenaille system consisted of redans, with salient angles of 6o° or more, flanking each other at right angles ; from which he gave to his system the name of "perpendicular fortification." Lazare Carnot (q.v.), the "Organizer of Victory," was, in fortifi cation, a follower of Montalembert, and produced in tenaille system on strong and simple lines.
Carnot was also, like Coehoorn, a great believer in the mortar; but while Coehoorn introduced the small portable mortar that bears his name, Carnot expected great results from a 13in. mortar throwing 600 iron balls at each discharge. He endeavoured to prove mathematically that the discharge of these mortars would in due course kill off the whole of the besieging force. These mor tars be emplaced in open fronted mortar casemates, in concealed positions. The main idea of Montalembert was that for a successful defence it was necessary for the artillery to be superior to that of the enemy. This idea led him to the adoption of casemates in several tiers ; in preference to open parapets, exposed to artillery fire of all kinds, high angle, ricochet and reverse. In considering the defects of bastions he had arrived at the conclusion that for flanking purposes two forms of trace were preferable ; either the tenaille form, or that in which the primary flanking elements, in stead of facing each other with overlapping fire, as with the bas tions, should be placed back to back in the middle of the exterior side. With his central flanking work Montalembert laid the foundation of the polygonal system.
Montalembert was one of the first to foresee the coming neces sity for detached forts, and it was for these that he chiefly pro posed to use his caponier flanking, preferring the tenaille system for large places. In abandoning the bastioned trace he was already committed to the principle of casemate defence for ditches. Mon talembert is said to have contributed more new ideas to fortifica tion than any other man; sometimes unsound, all the best work of the 19th century rests on his teaching. The Germans, who already used the tenaille system and made free provision of bomb-prod casemates, took from him the polygonal trace and the idea of the entrenched camp. The polygonal system in fortification implies straight or slightly broken exterior sides, flanked by casemated caponiers. The essence of the system is its simplicity, which allows of its being applied to any sort of ground, level or broken, and to long or short fronts.
France, for a few years after 1815, could spare little money for fortifications, and nothing was done but repairs and minor im provements on the old lines. Belgium, having some money in hand, rebuilt and improved in detail a number of bastioned fortresses which had fallen into disrepair. In 183o France began to follow the lead of Germany with entrenched camps. The enceinte of Paris was reconstructed, and detached forts were added. The Belgian and German frontiers of France being considered fairly protected by the existing fortresses, they turned their attention to the Swiss and Italian frontiers, and constructed three fortresses with de tached forts at Belfort, Besancon and Grenoble. The enceinte was simplified on account of the advanced defences. That of Paris, which was influenced by political considerations, was a simple bas tioned trace with rather long fronts and without outworks. As re gards the detached forts there was certainly a want of clearness of conception. Those of Paris were simply fortresses in miniature, square or pentagonal figures with bastioned fronts and containing defensible barracks.
While a great deal of work was done on these lines, a very active controversy had already begun on the general question as to whether guns should be employed in forts at all. Some declared that the accuracy and power of artillery had already developed so far that guns in fixed and visible positions would be put out of action in a very short time. The remedy proposed by these was the removal of the guns from the forts into "wing-batteries" which should be less conspicuous; but soon the broader idea was put forward of placing the guns in concealed positions and moving them from one to another by means of previously prepared roads or railways. Others declared that there was no safety for the guns outside the forts, and that the use of steel turrets and disappearing cupolas was the only solution of the difficulty. Gen. Brialmont, who had by this time become the first European authority on forti fication questions, ranged himself on the side of the turrets. The younger school, however, pinned their faith to mobility, and pleaded for it vehemently in numerous publications.