Chapter IX: Part 9

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 Marseilles, which extended from
the tower already described to the base of the tower of the city, was
60 ft. long, and built largely of great beams 2 ft. square, connected
by iron pins and bands. It was unusually narrow, the ground sills of
the side walls being only 4 ft. 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 up to 600 lb. weight, heavy darts
from 6 to 12 ft. long, and Greek fire. Archimedes at the siege of
Syracuse even made some throwing 1800 lb. The ranges varied, according
to the machine and the weight thrown, up to 600 yds. for direct fire
and 1000 yds. for curved fire. At the siege of Jerusalem Titus
employed three hundred catapults of different sizes and forty
balistae, of which the smallest threw missiles of 75 lb. weight. At
Carthage Scipio found 120 large and 281 medium catapults, 23 large and
52 small balistae, and a great number of scorpions and other small
missile engines.

Screens and mantlets for the protection of the engine-workers were
used in great variety.

In addition to the above, great mechanical skill was shown in the
construction of many kinds of machines for occasional purposes. A kind
of jib crane of great height on a movable platform was used to hoist a
cage containing fifteen or twenty 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 50 sq. ft., made up of 168 small
mirrors each 6 by 8 in., lead was melted at a distance of 140 ft. and
wood was set on fire at 160 ft.

The development of masonry in permanent fortification had long since
reached its practical limit, and was no longer proof against the
destructive methods that had been evolved. The extemporized defences
were, as is always the case, worn down by a resolute besieger, and the
attack was stronger than the defence.

Middle ages.

Through the dark ages the Eastern Empire kept alive the twin sciences of fortification and siegecraft long enough for the Crusaders to learn from them what had been lost in the West. Byzantium, however, always a storehouse of military science, while conserving a knowledge of the ancient methods and the great missile engines, contributed no new ideas to fortification, so far as we know. In practice the Byzantines favoured multiplied enceintes or several concentric lines of defence. This of course is always a tendency of decadent nations.

In the West the Roman fortifications remained standing, and the Visigoths, allies of Rome, utilized their principles in the defences of Carcassonne, Toulouse, &c. in the 5th century. Viollet-le-Duc's description and illustrations of the defences of Carcassonne will give a very good idea of the methods then in use:--

"The Visigoth fortification of the city of Carcassonne, which is still
preserved, offers an analogous arrangement recalling those described
by Vegetius. The level of the town is much more elevated than the
ground outside, and almost as high as the parapet walks. The curtain
walls, of great thickness, are composed of two faces of small cubical
masonry alternating with courses of brick; the middle portion being
filled, not with earth but with rubble run with lime. The towers were
raised above these curtains, and their communication with the latter
might be cut off, so as to make of each tower a small independent
fort; externally these towers are cylindrical, and on the side of the
town square; they rest, also towards the country, upon a cubical base
or foundation. We subjoin (fig. 1) the plan of one of these towers
with the curtains adjoining. A is the plan of the ground-level; B the
plan of the first storey at the level of the parapet. We see, at C and
D, the two excavations formed in front of the gates of the tower to
intercept, when the drawbridges were raised, all communication between
the town or the parapet walk and the several storeys of the tower.
From the first storey access was had to the upper crenellated or
battlemented portion of the tower by a ladder of wood placed
interiorly against the side of the flat wall. The external
ground-level was much lower than that of the tower, and also beneath
the ground-level of the town, from which it was reached by a
descending flight of from ten to fifteen steps. Fig. 2 shows the tower
and its two curtains on the side of the town; the bridges of
communication are supposed to have been removed. The battlemented
portion at the top is 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 and pulley. Fig. 3 shows the same
tower on the side towards the country; we have added a postern, the
sill of which is sufficiently raised above the ground to necessitate
the use of a scaling or step ladder, to obtain ingress. The postern is
defended, as was customary, by a palisade or barrier, each gate or
postern being provided with a work of this kind."

Meanwhile, in western Europe, siegecraft had almost disappeared. 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 Charlemagne and others 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 accordingly the sieges of that period dragged themselves out through long years, and if ultimately successful were so as a rule only through blockade and famine. It was not until the 11th century that siegecraft was revived in the West on the ancient lines.

Castles.

By this time a new departure of great importance had been made in the seigneurial castle (q.v.), which restored for some centuries a definite superiority to the defence. Built primarily as strongholds for local magnates or for small bodies of warriors dominating a conquered country, the conditions which called them into existence offered several marked advantages. The defences of a town had to follow the growth of the town, and would naturally have weak points. It was not to be expected that a town would develop itself in the manner most suitable for defence; nor indeed that any position large enough for a town could be found that would be naturally strong all round. But the site of a castle could be chosen purely for its natural strength, without regard, except as a secondary consideration, to the protection of anything outside it; and as its area was small it was often easy to find a natural position entirely suited for the purpose. In fact it frequently happened that the existence of such a position was the _raison d'etre_ of the castle. A small hill with steep sides might well be unapproachable in every direction by such cumbrous 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 conditions was practically impregnable; and this was the cause of the independence of the barons in the 11th 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 12th-century work is the Chateau Gaillard, built by Richard Coeur-de-Lion in 1196. This great castle, with ditches and escarpments cut out of the solid rock, and extensive outworks, was completed in one year. In the article CASTLE will be found the plan of the main work, which is here supplemented by an elevation of the donjon (or keep). The waved face of the inner or main wall of the castle, giving a divergent fire over the front, is an interesting feature in advance of the time. So also is the masonry protection of the machicolation at the top of the donjon, a protection which at that time was usually given by wooden hoardings. After the death of Richard, Philip Augustus besieged 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 abandoned 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 perhaps the greatest general of his time, exemplifies in its brief resistance the weak points of the designs of the 12th century. It is easy to understand how 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 development 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 protect 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 medieval 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 only 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. They were also fond of surprises, which the bad discipline of the time favoured.

We find, therefore, important progress in enlarging the area of defence and in improving arrangements for flanking. The size and height of all works were increased. The keep of Coucy Castle, built in 1220, was 200 ft. high. Montargis Castle, also built about this time, had a central donjon and a large open enclosure, within which the whole garrison 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, the influence of which lasted long after medieval times, towards complexity and multiplication of defences, to guard against surprise and localize successful assaults. Great attention was paid to the "step by step" defence. Flanking towers were cut off from their walls and arranged for separate resistance. Complicated entrances with traps and many doors were arranged. Almost all defence was from the tops of the walls and towers, the loopholes on the lower storeys being mainly for light and air and reconnoitring. Machicouli galleries (for vertical defence) were protected either by stone walls built out on corbels, or by strong timber hoardings built in war time, for which the walls were prepared beforehand by recesses left in the masonry. Loopholes and crenelles were protected by shutters. Great care and much ingenuity were expended on details of all kinds.

Already in the 12th century the engineers of the defence had made provision for countermining, by building chambers and galleries at the base of the towers and walls. Further protection for the towers against the pioneer attack was given by carrying out the masonry in front of the tower in a kind of projecting horn. This was found later to have the further advantages of doing away with the dead ground in front of the tower unseen from the curtain, and of increasing the projection and therefore the flanking power of the tower itself. The arrangement is seen in several of the towers at Carcassonne, and has in it the germ of the idea of the bastion.

The defences of Carcassonne, remodelled in the latter half of the 13th
century on the old Visigoth foundations, exemplify some of the best
work of the period. Figs. 5 and 6 (reproduced from Viollet-le-Duc)
show the plan of the defences of the town and castle, and a bird's-eye
view of the castle with its two barbicans. The thick black line shows
the main wall; beyond this are the lists and then the moat. It will be
noted that the wall of the lists as well as the main wall is defended
by towers. 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 defended by a labyrinth
of gates and flanking walls, which cannot be shown on this small
scale, and beyond these is a huge circular barbican in several
storeys, capable of holding 1500 men. 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 of the
general arrangement 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
communicating 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. Mining 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 sheltered 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 barrels 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. As Professor C.W.C. Oman has pointed out, the mechanical application of the three powers of tension, torsion and counterpoise (in the missile engines) had its limits. If these engines were enlarged they grew too costly and unwieldy. If they were multiplied it was impossible on account of their short range and great bulk to concentrate the fire of enough of them on a single portion of the wall.

Introduction of gunpowder.

It is difficult to give anything like an accurate account, in a small space, of the changes in fortification which took place in the first two centuries after the introduction of gunpowder. The number of existing fortifications that had to be modified was infinite, so also was the number of attempted solutions of the new problems. Engineers had not yet begun to publish descriptions of their "systems"; also the new names and terms which came into use with the new works were spread over Europe by engineers of different countries, and adopted into new languages without much accuracy.

Artillery was in use for some time before it began to have any effect on the design of fortification. The earliest cannon threw so very light a projectile that they had no effect on masonry and were more useful for the defence than the attack. Later, larger pieces were made, which acted practically as mortars, throwing stone balls with high elevation, and barrels of burning composition. In the middle of the 15th century the art of cannon-founding was much developed by the brothers Bureau in France. They introduced iron cannon balls and greatly strengthened the guns. In 1428 the English besieging Orleans were entirely defeated by the superior artillery of the besieged. By 1450 Charles VII. was furnished with so powerful a siege train that he captured the whole of the castles in Normandy from the English in one year.

But the great change came after the invasion of Italy by Charles VIII. with a greatly improved siege train in 1494. The astonishing rapidity with which castles and fortified towns fell before him proved the uselessness of the old defences. It became necessary to create a new system of defences, and, says Cosseron de Villenoisy, "thanks to the mental activity of the Renaissance and the warlike conditions prevailing everywhere, the time could not have been more favourable." There is no doubt that the engineers of Italy as a body were responsible for the first advance in fortification. There, where vital and mental energy were at boiling-point, and where the first striking demonstration of the new force had been given, the greatest intellects, men such as Leonardo da Vinci, Michelangelo and Machiavelli, busied themselves over the problem of defence.

It has been claimed that Albert Durer was the first writer on modern fortification. This was not so; Durer's work was published in 1527, and more than one Italian engineer, certainly Martini of Siena and San Gallo, had preceded him. Also Machiavelli, writing between 1512 and 1527, had offered some most valuable criticisms and general principles. Durer, moreover, had little influence on the progress of fortification; though we may see in his ideas, if we choose, the germ of the "polygonal" system, developed long afterwards by Montalembert. Durer's work was to some extent a connecting link between the old fortification and the new. He proposed greatly to enlarge the old towers; and he provided both them and the curtains with vaulted chambers for guns (casemates) in several tiers, so as to command both the ditch and the ground beyond it. His projects were too massive and costly for execution, but his name is associated with the first practical gun casemates.

Before beginning to trace the effect of gunpowder on the design 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 extended 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 provided trained and disciplined soldiers in large numbers.

When artillery became strong enough to destroy masonry from a distance two results followed: it was necessary to modify the masonry defences so as to make them less vulnerable, and to improve 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.

The bulwark.

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, which could be
destroyed even by the early light cannon-balls; and they offered at
the same time advanced positions for the guns of the defence. They
were found so useful for gun positions for flanking fire that later
they were placed in front of towers or at intervals along the walls
for that purpose.

This, however, was only a temporary expedient, and we have now to
consider the radical modifications in designs. These affected both the
construction and trace of the walls.

The wall.

The first lesson taught by improved artillery was that the walls
should not be set up on high as targets, but in some manner screened.
One method of doing this in the case of old works was by placing
bulwarks in front of them. In other cases the lists or outer walls,
being surrounded by moats, were already partially screened and
suitable for conversion into the main defence; and as with improved
flanking defence great height was no longer essential, the tops of the
walls were in some cases cut down. In new works it was natural to sink
the wall in a ditch, the earth from which was useful for making
ramparts.

As regards resistance to the effect of shot, it was found that thin
masonry walls with rubble filling behind them were very easily
destroyed. A bank of earth behind the wall lessened the vibration of
the shot, but once a breach was made the earth came down, making a
slope easy of ascent. To obviate this, horizontal layers of brushwood,
timber and sometimes masonry were built into the earth bank, and
answered very well (fig. 7).

Another expedient of still greater value was the use of counterforts.
The earliest counterforts were simply buttresses built _inward_ from
the wall into the rampart instead of _outward_ (fig. 8). Their effect
was to strengthen the wall and make the breaches more difficult of
ascent. An alternative arrangement for strengthening the wall was an
arched gallery built behind it under the rampart (fig. 9). This
construction was in harmony with the idea, already familiar, of a
passage in the wall from which countermines could be started; but it
has the obvious weakness that the destruction of the face wall takes
away one of the supports of the arch. The best arrangement, which is
ascribed to Albert Durer, was the "counter-arched revetment." This
consisted of a series of arches built between the counterforts, with
their axes at right angles to the face of the wall. Their advantage
was that, while supporting the wall and taking all the weight of the
rampart, they formed an obstacle after the destruction of the wall
more difficult to surmount than the wall itself and very hard to
destroy. The counter-arches might be in one, two or three tiers,
according to the height of the wall (figs. 10 and 11, the latter
without the earth of the rampart and showing also a countermine
gallery).

The rampart.

A more important question, however, than the improvement of the
passive defence or obstacle was the development of the active defence
by artillery. For this purpose it was necessary to find room for the
working of the guns. At the outset it was of course a question of
modifying the existing defences at as little cost as possible. With
this object the roofs of towers were removed and platforms for guns
substituted, but this only gave room for one or two guns. Also the
loopholes in the lower storeys of towers were converted into
embrasures to give a grazing fire over the ditch; this became the
commonest method of strengthening old works for cannon, but was of
little use as the resulting field of fire was so small. In some cases
the towers were made larger, with a semicircular front and side walls
at right angles to the curtain. Such towers built at Langres early in
the 16th century had walls 20 ft. thick to resist battering.

Even in new works some attempts were made to combine artillery defence
with pure masonry protection. The works of Albert Durer in theory, and
the bridge-head of Schaffhausen in practice, are the best examples of
this. The Italian engineers also showed much ingenuity in arranging
for the defence of ditches with masonry caponiers. These were
developed from external buttresses, and equally with the casemated
flanking towers of Durer contained the germs of the idea of
"polygonal" defence.

The natural solution, however, which was 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.

The _ditch_, which had only been occasionally used in ancient and
medieval fortification, now became essential and characteristic.
Serving as it did for 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 had
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 the counterscarp wall some of the earth
excavated from the ditch was piled up to increase the protection given
to the escarp wall. This earth was sloped down gently on the outer
side to meet the natural surface of the ground in such a manner as to
be swept by the fire from the ramparts and was called the _glacis_.

Now, however, a new difficulty arose. In all times a chief element in
a successful defence has consisted in action by the besieged outside
the walls. The old ditches, when they existed, had merely a slope on
the far side leading up to the ground-level; and the ditch was a
convenient place in which troops preparing for a sortie could assemble
without being seen by the enemy, and ascend the slope to make their
attack. The introduction of the counterscarp wall prevented sorties
from the ditch. At first it was customary, after the introduction of
the counterscarp, to leave a narrow space on the top of it, behind the
glacis, for a patrol path. Eventually the difficulty was met by
widening this patrol path into a space of about 30 ft., in which there
was room for troops to assemble. This was known as the _covered way_.

With this last addition the ordinary elements of a profile of modern
fortification were complete and are exemplified in fig. 12.

The trace.

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 introduction of ramparts and artillery made this more difficult in two ways. The rampart, interposed between the defenders and the face of the wall, put a stop to vertical defence. Also with the inferior gun-carriages of the time very little depression could be given to the guns, and thus the top of the enceinte wall, with or without a rampart, was not a suitable position for guns intended to flank the ditch in their immediate neighbourhood. The problem of the "trace" therefore at the beginning of the 16th century was to rearrange the line of defence so as to give due opportunity to the artillery of the besieged, both to oppose the besiegers' breaching batteries and later to defend the breaches. At the outset the latter role was the more important.

In considering the early efforts of engineers to solve this problem we must remember that for economical reasons they had to make the best use they could of the existing walls. At first for flanking purposes casemates on the ditch level were used, the old flanking towers being enlarged for the purpose. Masonry galleries were constructed across the ditch, containing casemates which could fire to either side, and after this casemates were used in the counterscarps. Some use was also made of the fire from detached bulwarks. It was soon realized, 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_ (which in its earliest shape suggests that it was in some sort the offspring of the barbican, placed to protect an entrance) gave plenty of space for guns, but 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 three hundred years, and so impressed itself on the imagination that to this day any strong advanced position in a defensive line is called by that name by unscientific writers. The word had been in use for a long time in connexion with extemporized towers or platforms for flanking purposes, 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. Fig. 13, taken from a contemporary MS. by
Viollet-le-Duc, shows a bastion added to the old wall of Troyes about
1528. On the other hand, in fig. 14 (taken from an English MS. of
1559, which again is based on the Italian work of Zanchi published in
1554), we find _a a_ spoken of as "bulwarks" and _b b_ as
"bastilions." The triangular works between the bastilions are
described as "ramparts," intended to protect the curtains from
breaching fire. (We may also notice in this design the broad ditch,
the counterscarp with narrow covered way, and loopholes indicating
counterscarp galleries.)

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, and it thus reverted to its original defensive intention. The term "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. Flanks retired, casemated or open, or sometimes in several tiers were proposed in infinite variety.

Thus, while in the early part of the 16th 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:--

1. The _cremaillere_ or indented trace: Faces and flanks succeeding
each other in regular order (fig. 15).

2. The _tenaille_ trace: Flanks back to back between the faces (fig.
16). The development of the flanks in this case gives us the _star_
trace (fig. 17).

3. The _bastioned_ trace: Flanks facing each other and connected by
curtains (fig. 18).

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.

The bastioned trace.

Here was therefore the parting of the ways. For those who objected to casemate fire, the bastioned trace was the way of salvation. They were soon in the majority; perhaps because the symmetry and completeness of the idea captivated 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 18th century. The Italian engineers, who were supreme throughout most of the 16th century, started it; the French, who took the lead in the following century, developed it, and officially never deserted it until late in the 19th century, when the increasing power of artillery made enceintes of secondary importance.

It will be useful at this point to go forward a little, with a couple
of explanatory figures, in order to get a grasp of the component parts
of the bastioned trace as ultimately developed, and of its outworks.

In fig. 19 ABCD represents part of an imaginary line drawn round the
place to be fortified, forming a polygon, regular or irregular.

ABC is an _exterior angle_ or angle of the polygon.

BC is an _exterior side_.

_zz_ is an _interior side_.

_abcdefghijk_ is the trace of the _enceinte_.

_bcdef_ is a _bastion_.

_zdef_ is a _demi-bastion_.

_de_ is a _face_ of the bastion.

_ef_ is a _flank_ of the bastion.

_fg_ is the _curtain_.

_bf_ is the _gorge_.

(Two demi-bastions with the connecting curtain make the bastioned
front, _defghi_.)

_zd_ bisecting the _exterior angle_ ABC is the _capital_ of the
bastion.

_xy_ is the _perpendicular_, the proportionate length of which to the
exterior side BC (usually about one-sixth) is an important element of
the trace.

_ef_C is the angle of _defence_.

BC_f_ is the _diminished angle_.

_cde_ is the _flanked angle_ or _salient angle_ of the bastion.

_e_ is the _shoulder_ of the bastion.

_def_ is the _angle of the shoulder_.

_efg_ is the _angle of the flank_.

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. 20, reproduced from a French engraving of 1705, shows an
imaginary place fortified as a hexagon with bastions and all the
different kinds of outworks then in use. The following is the
explanation of its figuring and lettering.

1. _Flat bastion:_ Placed in the middle of a curtain when the lines of
defence were too long for musketry range.

2. _Demi-bastion:_ Used generally on the bank of a river.

3. _Tenaille bastion:_ Used when the flanked angle is too acute; that
is, less than 70 deg.

4. _Redans:_ Used along the bank of a river, or when the parapet of
the covered way can be taken in reverse from the front.

A, B. _Ravelins._

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._

F. _Double tenaille_ (see L and M).

(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 pretre_. Such works
were rarely used.)

H. _Hornwork:_ Much used for gates, &c.

I. _Crown-work._

K. _Crowned hornwork._

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-lune lunettee_, the ravelin N being
protected by two counterguards, O.

P. _Re-entering places of arms._

Q. _Traverses._

R. _Salient places of arms._

S. _Places of arms_ without _traverses_.

T. Orillon, to protect the flank V.

X. A _double bastion_ or _cavalier_.

Y. A _retrenchment_ with a ditch, of the breach Z.

&. _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 attempt 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 prolongation 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 (fig. 21). Here we have faces, flanks and curtain in due proportion; the faces long enough to contain a powerful battery, and the flanks able to defend both curtain and faces. 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.

The 16th century.

In the systems published by Speckle of Strassburg in 1589 we find a distinct advance. Speckle's actual constructions in fortification are of no great importance; but he was a great traveller and observer, and in his work, published just before his death, he has evidently assimilated, and to some extent improved, the best ideas that had been put forward up to that time.

Two specimens from Speckle's work are well worth studying as connecting links between the 16th and 17th centuries.

Fig. 22 is early 16th-century work much improved. There are no
outworks, except the covered way, now fully developed, with a battery
in the re-entering place of arms. The bastions are large, but the
faces directed on the curtain get little protection from the flanks.
To make up for this they are flanked by the large cavaliers in the
middle of the curtain. The careful arrangement of the flank should be
noted; part of it is retired, with two tiers of fire, some of which is
arranged to bear on the face of the bastion. The great saliency of the
bastion is a weak point, but the whole arrangement is simple and
strong.

In the second example, known as Speckle's "reinforced trace" (fig.
23), we find him anticipating the work of the next century. The
ravelin is here introduced, and made so large that its faces are in
prolongation of those of the bastions. Speckle's other favourite
ideas are here: the cavaliers and double parapets and his own
particular invention of the low batteries behind the re-entering place
of arms and the gorge of the ravelin. These low batteries did not find
favour with other writers, being liable to be too easily destroyed by
the besiegers' batteries crowning the salients of the covered way.

Speckle's book is of great importance as embodying the best work of
the period. His own ideas are large and simple, but rather in advance
of the powers of the artillery of his day.

The 17th century.

At the beginning of the 17th century we find the Italian engineers following Paciotto in developing the complete bastioned trace; but they got on to a bad line of thought in trying to reduce everything to symmetry and system. The era of geometrical fortification (or, as Sir George Clarke has called it, "drawing-board" fortification) had already begun with Marchi, and his followers busied themselves entirely in finding geometrical solutions for the application of symmetrical bastioned fronts to such imaginary forms of perimeter as the oval, club, heart, figure of eight, &c. Marchi, however, was one of the first to think of prolonging the resistance of a place by means of outworks such as the ravelin. De Villenoisy says that Busca was the first to discuss the proportions and functions of all the component parts of a front; and Floriani, about 1630, was the last of the important Italians. The characteristics of a good deal of Spanish fortification carried out at this time were, according to the same authority, that the works were well adapted to sites, and the masonry excellent but too much exposed, while the bastions were too small. The Dutch and German schools will be referred to later.

The French engineers now began to take the lead in adapting the principles already established to actual sites. In the first half of the century the names of de Ville and Pagan stand out as having contributed valuable studies to the advancement of the science. In putting forward their designs they discussed very fully such practical questions as the length of the line of defence, whether this should be governed by the range of artillery or musketry fire, the length of flanks, the use in them of orillons, casemates and retired flanks, the size of bastions, &c.

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, some of them priests who were engaged in educating the sons of the upper classes, and who had to teach the elements of fortification among other things. They naturally wrote treatises, which were valuable for their clearness of style; and with their industry and ingenuity the elaboration of existing methods was a very congenial task. Most of these essays took the form of multiplication and elaboration of outworks on an impossible scale, and they culminated in such fantastic extravagances as the system of Rhana, published in 1769 (fig. 24). These proposals, however, were of no practical importance.

Vauban.

The work of the real masters who knew more than they published can always be recognized by its comparative simplicity. The greatest of these was Sebastien le Prestre de Vauban (q.v.). Born in 1633, and busied from his eighteenth year till his death in 1707 in war or preparations for war, he earned alike by his genius, his experience, his industry and his personal character the chief place among modern military engineers. His experience alone puts him in a category apart from others. Of this it is enough to say that he took part in forty-eight sieges, forty of which he directed as chief engineer without a single failure, and repaired or constructed more than 160 places. Vauban's genius was essentially practical, and he was no believer in systems. He would say, "One does not fortify by systems but by common sense." Of new ideas in fortification he introduced practically none, but he improved and modified existing ideas with consummate skill in actual construction. His most original work was in the attack (see below), which he reduced to a scientific method most certain in its results. It is therefore one of the ironies of fate that Vauban should be chiefly known to us by three so-called "systems," known as his "first," "second" and "third." How far he was from following a system is shown by de Villenoisy, who reproduces twenty-eight fronts constructed by him between 1667 and 1698, no two of which are quite alike and most of which vary very considerably to suit local conditions.

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 (1684-1688), obviously suggested by a design of Castriotto's one hundred 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 the Royal Military Academy text book of fortification (fig. 25) as typical of much of Vauban's work. It may be observed that 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. Sometimes it has flanks and occasionally a keep.

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. Fig. 25 shows two forms. In both the parapet of the tenaille had to be kept low, so that the flanks might defend a breach at the shoulder of the opposite bastion, with artillery fire striking within 12 ft. of the base of the escarp. 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.

For the construction of the trace an average length of about 400 yds.
(which, however, is a matter entirely dependent on the site) may be
taken for the exterior side. The perpendicular, except for polygons of
less than six sides, is one-sixth, and the faces of the bastions
two-sevenths of the exterior side. The flanks are chords of arcs
struck from the opposite shoulder as centres. An arc described with
the same radius, but with the angle of the flank as a centre, and
cutting the perpendicular produced outwardly, gives the salient of the
ravelin; the prolongations of the faces of the ravelin fall upon the
faces of the bastions at 11 yds. from the shoulders. The main ditch
has a width of 38 yds. at the salient of the bastions, and the
counterscarp is directed upon the shoulders of the adjoining bastions.
The ditch of the ravelin is 24 yds. wide throughout.

As regards the profile the bastions and curtain have a command of 25
ft. over the country, 17 ft. over the crest of the glacis and 8 ft.
over the ravelin. The ditches are 18 ft. deep throughout. The parapets
are 18 ft. thick with full revetments. In his later works he used
demi-revetments.

Fig. 26 shows the tower bastions of Neu-Breisach, or the so-called "third system." It is worth introducing, simply as showing that even a mind like Vauban's could not resist in old age the tendency to duplicate defences. Here the main bastions and tenaille are detached from the enceinte. The line of the enceinte is broken with flanks and further flanked by the towers. The ravelin is large and has a keep. The section through the face of the bastion shows a demi-revetment with wide berm, and a hedge as an additional obstacle.

18th and 19th centuries.

After Vauban died, though the theories continued, the valuable additions to the system were few. Among his successors in the early part of the 18th century Cormontaingne (q.v.) has the greatest reputation, though his experience and authority fell far short of Vauban's. He was a clear thinker and writer, and the elements of the system were distinctly advanced by him. His trace includes an enlarged ravelin with flanks, the ends of which were intended to close the gaps at the end of the tenaille, and a keep to the ravelin with flanks. He provides a very large re-entering place of arms, also with a keep, the ditches of which are carefully traced so as to be protected from enfilade by the salients of the ravelin and bastion. He was also in favour of a permanent retrenchment of the gorge of the bastion. His works were printed, with many alterations, more than twenty years after his death, to serve as a text-book for the school of Mezieres. This school was established in 1748, and from this time forward there was an official school of thought, based on Vauban. Cormontaingne's work, therefore, represents the modifications of Vauban's ideas accepted by French engineers in the latter part of the 18th 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 firearms, we find the main elements of the bastioned system remaining unchanged right up to the period of the Franco-German War in 1870. Chasseloup-Laubat tells us that, before the Revolution, to attempt novelties in fortification was to write one's self down ignorant. How far the general form of the bastion with its outworks had become crystallized is evident from a cursory comparison of fig. 27 with Vauban's early work. This figure is the front of the Metz school in 1822, by General Noizet.

Since, therefore, the official view was that the general outlines of the system were sacred, the efforts of orthodox engineers from Cormontaingne's time onwards were given to improvements of detail, and mainly to retard breaching operations as long as possible. We find enormous pains being bestowed on the study of the comparative heights of the masonry walls and crest levels; with the introduction here and there of glacis slopes in the ditches, put in both to facilitate their defence and to protect portions of the escarps.

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 improve 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 outside 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. It is probable that this system would
have lent itself to a splendid defence by an able commander with a
strong force; but under the opposite conditions it has a dangerous
element of weakness.

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 650 yds. 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 defence, and
the portion next the salient, up to about 80 yds. 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.

Fig. 28 shows a half front of Chasseloup's system, of ordinary length,
as actually constructed. The section shows an interesting detail, viz.
the Chasseloup mask--a detached mask with tunnels for the casemate
guns to fire through, the intention of which is to save them from
being destroyed from a distance.