Siege Warfare 1500-1830

The Surrender of Breda by Diego Velázquez. Oil on canvas, 1635.

Map of the siege of Breda by Spinola. J.Blaeu.

If gunpowder revolutionized combat, its effect upon siege operations was equally well recognized by contemporaries. Beginning in the sixteenth century, much ink had already been spilled to analyze the competition between fortress and cannon, a subject which for a time became part of the normal education of a gentleman. Later during the eighteenth century, the scope of the debate was immensely broadened as it came to be realized that the effects of that competition were not limited to the military field but led to far-reaching social, economic, and political changes as well. It was argued, and has been ever since, that the castle was defeated by the gun and that feudalism came crashing down as one of the results. This interpretation is, however, open to question.

The introduction of firearms to Europe dates back to the first quarter of the fourteenth century. The earliest were apparently used against personnel rather than against fortifications, the effect being as much psychological as physical. While the first record of an association between cannon and a castle dates to within thirty years of artillery…s first appearance, it may be significant that this record tells us of a cannon that was used not to attack a fortress but to defend it. In 1356, an English garrison in Breteuil, Normandy, was being besieged by a French army under the command of King John II. Employing the usual techniques of the age, the French filled in the moat, crossed it, and then brought a fighting tower, or belfry, to the wall. The defenders at first engaged the assaulting party hand to hand, but then suddenly withdrew to allow some form of fire-engine to be used. The text of Froissart, who is our source for this episode, is not clear. While he seems to mention cannon that threw “heavy bolts,” in the same breath he also refers to “jets of fire” which were somehow produced and used to set the tower alight. Whatever his exact meaning, the first recorded use of what may have been artillery in connection with siege warfare ended with a temporary victory for the defense since the French tower caught fire and its remains had to be abandoned in the moat. A few days after this episode, the French king felt threatened from a different quarter and became impatient to end the siege. He offered terms, and Breteuil surrendered.

From this point onward, accounts of cannon being used both to attack fortresses and to defend them multiply rapidly. The Crònica di Pisa, written late in the fourteenth century, narrates that the Pisans in 1362 used a bombard weighing almost 1000 kg against the castle of Pietra Buona. However, there is no record of its effect on the wall. In 1357 the Duke of Burgundy employed guns—borrowed, interestingly, from the municipality of Chartres—to capture the castle of Camrolles near that town. Twelve years later the municipality of Arras made provision for protecting the town gates by allocating a cannon to each of them. During the siege warfare that took place between Venetians and Genoese in 1379-80—the war of Chiogga—there was much use of bombards by both sides. As in the case of ballistae and catapults in ancient times, artillery could be made to face both ways and this was actually done almost from the beginning.

The earliest cannon also resembled previous siege engines in another respect. Insufficiently powerful to bring down curtain walls, their main use was to clear the defenders from sections of the wall so as to permit mining, boring, or the approach of siege towers. As time went on, the size and power both of individual cannon and of siege trains gradually increased, however, and this made it possible to develop new tactics. Froissart narrates that, for the Siege of Odkruik in 1377, the Duke of Burgundy marshaled no fewer than 140 cannon. Some of them fired stone projectiles 100 kg in weight, corresponding to a 35-centimeter bore. This appears to be the first case on record when artillery succeeded in making a breach in the fortifications, whereupon the castle surrendered. As compared to earlier stone-throwing engines, the ability of cannon to bring about this result probably depended not so much on their power as in the flatter trajectory that they afforded. This made it possible to aim at specific points on the wall and hit them again and again, thus ultimately bringing about a collapse.

The curtain walls surrounding medieval castles were singularly ill-suited to resist artillery fire. Since they were made tall to withstand an escalade, they presented excellent targets. They were designed to withstand boring and ramming, so they were frequently much thinner on top than at the base. A besieger who knew his business might therefore use his artillery to bring the higher masonry crashing down upon the lower, thus simultaneously creating a graduated passage for an assault. Once an effective method for creating a breach was available, crossing the moat that protected most castles became much easier, since it would tend to be filled in by the ruins of the walls themselves. Finally, since curtain walls were high and narrow on top, guns could only be used in their defense with great difficulty, if at all.

In so warlike an age as the late European Middle Ages, these shortcomings were quickly realized. Attempts were accordingly made to modify existing structures, a process which involved several distinct steps. During the opening years of the fifteenth century, gates were already being protected from the rear by the cutting of broad passages known as boulevards (from bouleverser, literally, to bowl over) which offered a free field for the fire of cannon. Next, towers were cut down and filled in with earth so as to create a platform for other cannon which were trained outward. Since the towers of medieval castles were for the most part too cramped to serve this purpose, however, the attempt to provide platforms was soon transferred to the curtain walls themselves. Their height was reduced and they were backed up with massive earthen ramps, an operation sufficiently commonplace to acquire a technical term (“rampiring”) of its own. Though rampiring helped castles to withstand an artillery bombardment, it also carried the disadvantage of causing walls to collapse outward once the breach was made, thus facilitating assault and entry. The entire process was makeshift by nature, and is perhaps best understood as an attempt to save the huge social and economic investment represented by castles.

Side by side with these expedients, during the late fourteenth century attempts were already being made to construct new fortifications which would be impervious to cannon. First, it was necessary to build the walls in such a way as to enable them to withstand a bombardment. Second, room had to be provided for the use of artillery by the defenders themselves. In Italy, France, and England, the first response to this dual demand was to lower the walls and thicken them, in some cases to as much as 15-20 meters. Next came the abandonment of towers in favor of round, tublike structures known as roundels and described by Albrecht Duerer and others. The roundel…s walls differed from those of the tower in that they no longer stood vertical to the ground, but were inclined inward in order to present glancing surfaces for shot. Not only did their flat tops provide a platform for guns, but it did not take long before the walls came to be equipped with built-in embrasures and vaulted casemates. Pointing their cannon outward from these, gunners attempted to create interlocking fields of fire to avoid dead corners. These innovations notwithstanding, late fifteenth century fortresses resembled their predecessors in that they stood out high above the ground. The idea that tall is strong had entrenched itself from time immemorial, and it naturally took a while to be abandoned.

When Charles VIII invaded Italy in 1494 he brought along an unprecedentedly strong siege train that was the wonder of the age. The most modern fortresses he encountered were of the type described above. As Machiavelli derisively says in The Prince, they were brought down “chalk in hand,” by which he apparently meant that it was sufficient for a French officer to make a mark on a fortress gate for its garrison to surrender in short order. As so frequently happens in war, however, the success of one side—in this case, the attack—was short-lived. The reaction when it came was strong and effective. In the first decade of the sixteenth century, the Pisans and Venetians had already adopted the device of separating their interior ramparts from the outer walls by a ditch. As a result, when the outer wall collapsed it formed a barrier made of jagged stone unmixed with earth, and this barrier came directly under the muzzles of the cannon stationed on the overlooking ramparts behind. In 1504 it was this system which enabled Pisa, a small and weak town, to withstand a French siege employing the most advanced means then available. The potential of the new method was demonstrated even more dramatically in 1509 when the Empire, France, and the Papal State formed an unholy Alliance whose objective was to dismember Venice. The result was a siege at Padua, a siege which ended with the withdrawal of the attackers, partly because of the strength of the fortifications, and partly because the German nobility refused to dismount and fight on foot.

The so called “Pisan rampart,” however, proved to be only a foretaste of things to come. For a time, after 1510, there was much experimentation with fortifications made of earth and wood. In 1555, during the Spanish siege of Santhia in Piedmont, a fort of this kind absorbed several thousand roundshot and emerged intact. Meanwhile, Italian engineers such as Antonio da Sangallo and Michele di Sanmicheli were hard at work looking for a permanent solution. Sometime around 1520—although certain forerunners can be traced as early as the 1470s or 1480s—the so-called “Italian” type of fortification emerged, a revolutionary innovation which had the effect of enormously strengthening the defense.

The new system of fortification consisted of three simple elements. First, the entire structure was now built right into the immensely wide ditch, with the result that it no longer projected much above ground and consequently no longer presented a target to the attacker…s artillery. Second, a combination of long, straight walls with squat, wedge shaped towers (bastions) permitted the entire length of the ditch to be raked by the fire of cannon that were either trained through especially-constructed embrasures or else were mounted atop the low, flat walls. Third, it was realized almost from the beginning that the bastions could be made to protect not only the walls but also each other. This demanded that they be placed in symmetrical order, with blunt angles pointing outward in every direction. This created the characteristic star-like shape of fortifications, hundreds of which were to dot the European countryside. Naturally, the new arrangements did not emerge all at once. However, by 1560 every one of the essential elements was to be found in the work of a man like Francesco Paciotto da Urbino, who was responsible for the fortification of Turin.

Over the next three centuries, the new type of fortress spread from Italy into France, England, Germany and, above all, the Low Countries, where a triple line of these structures, situated on the Great Rivers and adapted to local conditions, enabled the Dutch Revolt to survive and triumph. Driven partly by the practical challenge presented by the ever growing power of the offense, but partly also by the natural ingenuity of engineers always on the lookout for new problems to solve, fortifications developed in two principal directions. First, the gradually increasing range of cannon caused fortifications to grow larger and more expensive. Second, they began to sprout outworks, which would make it more difficult for the attacker to bring his artillery within range. Initially these outworks consisted of isolated bastion-like structures so situated as to protect each of the star…s points. However, it was not long before attempts were made to incorporate outworks and fortress into a single structure, which then led to the construction of even further outworks. Over time, the process could repeat itself several times.

Thus, by the early seventeenth century, fortresses had become immensely complicated affairs made up of a bewildering array of elements. Bastions and outworks alike were provided with ravelins and redoubts, bonettes and lunettes, tenailles and tenaillons and counterguards, hornworks and crownworks. Approaching them from the outside, the traveler would be met by covered roads and cuvettes and fausse brayes and scarps, not to mention cordons and banquettes and counterscarps. Many of these elements were difficult to keep apart, not only for us but also for contemporaries who, like Uncle Toby in Tristram Shandy, sometimes covered the whole lot with ridicule. Though the basic principles were the same everywhere, a very large number of variations developed to suit national tastes as well as the peculiarities of the terrain. Naturally, most military architects were run-of-the-mill and content to follow the immense number of handbooks in circulation. However, here and there celebrated architects such as Paciotto, Coehorn, and Vauban developed their own distinctive styles, adding still further to the confusion while at the same time providing additional models for imitation.

The fact that fortresses developed in this way, of course, is itself an indication that offense, and the technological means on which it rested, did not stand still. Though neither cannon nor their ammunition changed much after 1550, artillery did tend to become more powerful. The greatest progress was made in the organization and systematization of siege warfare. The late sixteenth and early seventeenth centuries saw the emergence of well-defined procedures for investing, besieging, and attacking a fortress. Over time, these procedures tended to harden and to assume something of the character of a ritual dance consisting of precisely regulated moves and countermoves.

Arriving on the location, the first task to be performed by the commander of an attacking army was to surround the town and cut off its approaches. This having been achieved, and attempts to obtain the garrison…s surrender having failed, the next step was to reconnoiter the terrain to discover the spot most suitable for the emplacement of siege artillery. The first line of parallel trenches would be opened and the guns, often protected by portable earth-filled wickerwork structures, stationed in place. A steady bombardment would drive the defenders off the section of the walls directly opposite, and so enable the attackers to advance towards the fortress by digging zigzag trenches. At a certain distance, a second parallel trench would be opened. The guns were then dragged forward, and the process repeated. Unless it was interrupted by the defenders, who sometimes dug their own trenches in order to reach the enemy and dislodge him, two or three forward bounds of this kind usually brought the guns within range and permitted the actual process of breaching the walls to begin. Once a breach was made, the place would be entered by assault. Allowing for varying local conditions, a skilled commander such as Vauban could calculate the duration of a siege almost to the day, and so of course could the defenders. Consequently the process of surrendering fortresses with honor developed into a fine art, surrounded by elaborate ceremonies and books of rules.

Although some of the older techniques of siege warfare, such as boring and ramming or the use of towers, had entirely disappeared by the middle of the sixteenth century, others still remained in use. Chief among those was the ancient principle of throwing up a wall, or vallation, to prevent sorties and cut off the garrison from the surrounding countryside. This in turn was sometimes surrounded by a second wall, known as countervallation and aimed at frustrating any attempts at relief. While artillery eventually came to present the most important means for breaching fortifications, mining and countermining continued to be used, and their effectiveness was increased by the use of gunpowder as an explosive. Escalading a fortress was still sometimes possible, whereas at other times attempts were made to gain entry by all kinds of underhanded means. Above all, siege operations continued to be conducted at such close quarters that both sides were often able to exchange taunts, promises, and threats, using arrows (until 1600) to shoot messages, or simply shouting at one another. As has always been the case in war—and never more so than during the confused seventeenth century and the cosmopolitan eighteenth—attackers and defenders freely imitated each other…s methods. Partly as a result, the race between them was neck-and-neck and was never really decided in favor of one side or the other.

Seen from a wider point of view, not only the techniques of siege warfare but the concept of the siege itself remained essentially the same. Although the most powerful fortresses no longer stood out high above the surface but were partly hidden in the ground, they continued to consist of enceintes designed to repulse assault and keep the attackers out. Conversely, siege warfare still aimed at first cutting the defenders off from the surrounding country and then either breaking into the ring or starving them out. Particularly during the age of religious wars between 1550 and 1650, fortresses kept their traditional function as places of refuge. Since the effective range of cannon still did not exceed 1200 meters or so, each fortress represented a stronghold in its own right and there could be no question of building them close enough to each other to offer mutual support by fire. Here and there entire belts of fortresses were constructed to cover all possible approaches into a country; they did not, however, link up into continuous barriers of the kind that have become so familiar since World War I. Since fortresses were very numerous, the role that they played in strategy was if anything greater than it had been even in the Middle Ages. During the period from 1560 to 1700 in particular, warfare consisted less of battles in the open field than of an endless succession of sieges. One early eighteenth-century authority even calculated that there were three sieges for each battle, not counting cases in which fortresses were besieged unsuccessfully.

Thus, the common view that the advent of cannon changed the balance between the attackers and the fortified defense is simply not supported by the evidence. In truth, the two progressed very much together. Often, the very same engineers who built the most powerful fortresses were also responsible for devising the most sophisticated methods for attacking them, the great Vauban being an outstanding if by no means unusual example of this. Since the length of sieges varied enormously, it would be all but impossible to prove that fortresses were becoming easier or more difficult to capture. The supposed advantage of the attackers over the defense cannot have been very apparent to Charles the Bold of Burgundy, who besieged the town of Neuss for a whole year (1475-76) before finally being obliged to withdraw. Riga in 1700 held out for seven months, Milazzo in 1718-19 for just as long. At the other extreme, ruses and bribes sometimes enabled towns such as Mons (1691) and Huy (1705) to be taken within a matter of days. Most sieges probably fell into the 40-60 day category. To quote Vauban, a resistance lasting 48 days could be regarded as respectable.

In the absence of detailed statistics, the growth in the power of the offensive cannot be proved. Rather, the most important effect of artillery upon siege warfare seems to have lain in a different sphere, namely the greatly enhanced scale on which fortresses had to be built and siege operations conducted. Since cannon, by the middle of the fifteenth century, had outstripped the largest siege engines in point of both power and range, the enceintes built to withstand them had to be that much larger and possess far thicker walls. Such structures in turn called for garrisons numbering in the thousands, sometimes more, and also for much increased quantities of stores and ammunition of every kind. Conversely, attacking a first class fortress was by no means a simple operation logistically. To do so it was necessary to concentrate a large force at a single spot and keep it fed over a period of weeks, if not months. Taking the minimum figures of 1.5 kg per day per man and 15 kg per day per horse, and employing the estimate of a contemporary expert. Puysegur, of two horses for every three men, the daily requirement for feeding an army of 50,000 troops would amount to approximately 475 tons. Though the quantity of powder, ammunition, and engineering materials needed for a siege only amounted to a fraction of this, in absolute terms it too could be very large.

Thus, the principal effect of the advent of artillery and the concommitant advances in fortification was to make both the attack and the defense of fortresses very much more complicated and expensive. Gone were the days when every prince, baron, or monastery could surround themselves with thick walls which, if never altogether impregnable, were at least able to force a considerable delay on an attacker. Gone, too, were the days when the most important arms, or at least some fairly effective arms, could be made by the village blacksmith. Instead, military technological progress created a situation where warfare in general, and fortress warfare in particular, came to demand a combination of financial muscle, bureaucratic organization, and technical expertise. All of these were to be found less in the feudal countryside than in the bourgeois-capitalist town economy which, spreading from south to north and from west to east, played an ever-increasing role.

In their opposition to the nobility both of Church and State, the burghers of the towns found useful allies in the monarchies. The monarchs were the only ones who could afford to build and maintain cannon. Consequently, their power grew and grew until it became absolute. Ultimately the net effect of these developments was a great increase in the minimum size necessary to make political units militarily viable. Instead of being a pastime for individual lords who relied on their vassals, or else an expedient used by towns which called out the citizen-body, the conduct of warfare tended to become centralized in the hands of kings and later in those of national states.

While the trend towards larger political units capable of sustaining the new scale of war in all its forms was both marked and steady, it was by no means simple or linear. The period from about 1450 to 1650 was as unsteady politically and marked by as many wars as any during the Middle Ages. So many peasant uprisings and national revolts and religious conflicts and civil wars were taking place that very often even contemporaries were unable to discover who was fighting whom, let alone what for. Though sieges were frequent, small-scale guerrilla warfare was endemic in the countryside between the fortresses. Often it was all but indistinguishable from simple brigandry. In the hands of military contractors such as the seventeenth-century commander Wallenstein, war itself for a time was turned into a form of self-sustaining capitalist enterprise which promised riches and even principalities to the most successful practitioners. Whether this situation reflected the dominance of offense over defense, or the other way around, is difficult to say. In any case, military technology was but a single factor among the many that were involved. War is too complex a tapestry to be dominated by a single thread, however thick and however brilliant.

A new equilibrium was established during the second half of the seventeenth century. With armies becoming increasingly professional, the role of irregular warfare declined, though it never disappeared altogether. Fortresses and siege operations continued to be vital constituents of war. Though the scale of both had greatly increased and was still increasing, few if any new principles were added, so that even as late as 1832 the French army during the siege of Antwerp was found reading Vauban and employing the traditional methods. Long before this time, the borders of the most important states had come to be protected by double and sometimes triple belts of these structures. Partly as a result, the complete conquest and subjugation of one country by the other was generally regarded as no longer practicable. A new political order, based on an acknowledged, if dynamic, balance of power, was created and maintained itself. Entire countries were turned into quasi-fortresses, protected as they were by brick strongholds covering the best approaches, and held together by roads and later by railroads. Thus a clear separation between “front” and “rear” was created, acting as one of the factors behind the development of the modern distinction between combatants and noncombatants. This, in turn, lasted until the invention of aircraft. By enabling armed forces to overfly national borders and penetrate into the enemy…s soft interior, aircraft led to the breakdown of hitherto prevailing international law, a breakdown with which we are still trying to contend.

Within each state separately, artillery not only helped royal power assert itself against all competitors but actually turned into its symbol. Cannon fired salutes when princes were born, decorated their palaces while they reigned, and increasingly figured in their funerals when they died. Louis XIV even caused his guns to be emblazoned with the words ultima ratio regis, which was an accurate if cynical description of their function. While kings played with real cannon, lesser mortals often did the same with custom-made smaller versions or, failing this, had models placed on the mantelpiece. Such martial displays notwithstanding, warfare continued to be dominated as much by humdrum nonmilitary technology as by spectacular fortresses and cannon. Ultimately, it was developments in nonmilitary technology that accounted for the revolution in strategy usually associated with the name of Napoleon Bonaparte.