Castles, Battles, and Bombs: How Economics Explains Military History by Jurgen Brauer and Hubert van Tuyll, an excerpt

Historians may cringe, but the popular “castle and knight” image of the High Middle Ages does contain important elements of truth. Certainly, warfare was constant. To denizens of the twenty-first century, the scale of war a thousand years ago appears small, but the share of resources that was consumed by war was enormous. This consumption included not only the expenses of waging war but, almost invariably, the deliberate destruction of economic assets that accompanied invasions, and sometimes retreats as well. Power lay with substantial property owners. In the absence of powerful centralized governments local rulers could and did make war for almost every reason imaginable. To be sure, tradition, chivalry, and (occasionally) law did place some limits on warfare, but it was almost impossible for any medieval ruler of substance to avoid fighting for his entire career.

Few were disposed to try. Trained from boyhood in the ways of war, even the less aggressive were rarely inclined to surrender territory or privileges just to avoid fighting. This did not mean that the decision to fight could be made casually or irrationally. As any economist will remind us, resources are always limited and placed on medieval rulers a far more stringent constraint than is the case today. A modern state possesses impressive tools to wage war such as a national tax system, conscription, and credit. None of these existed a thousand years ago. Rulers might tax, but neither economic reality, administrative capacity, nor tradition would allow collections anywhere near as extensive or methodical as today. Conscription was unknown. True, men could be ordered to wage war, but only for periods specified by tradition. And credit on a scale fit to serve an entire nation only began to appear late in the thirteenth century and was not, at any rate, a realistic option for lesser nobles. A king in 1008 was far more aware of the need to make choices than a president in 2008.

Decision making under constraints is the provenance of economics, and the decisions of medieval rulers regarding war form a fertile area for the study of the making of choices. Potentially, here we have a marvelous case for examining whether military history is amenable to economic analysis. The pithy popular image of the age—castles and knights—is actually helpful, even if the conjunctive and some of the details are wrong. For when it came to expenditure the ruler had but one stark choice: fortify or hire, that is, to build castles or recruit armies.

Although the medieval army was sometimes regarded as an almost irrelevant rabble among whom only the mounted knights truly mattered, recent scholarship has changed our view significantly. The dominance of the mounted knight in particular has been questioned. As we shall see, the armored man on horseback was of no use whatsoever attacking a castle. Even with regard to the battlefield the picture has changed: “The notion that the medieval knight, his lance couched beneath his right arm, his shield and reins in his left hand, dominated military planning and strategy during this period is the stuff of epic poetry.” The medieval army was much more, and much more complicated, than the knightly armored cavalry alone. The cavalry’s primacy has been exaggerated. Some of these misunderstandings were exacerbated by the fact that, unlike their rulers, the commanders of the age offered battle infrequently. Medieval armed forces maneuvered, ravaged, and besieged more often than they fought each other in the open field. This was the result of a rather methodical and careful approach to military strategy but had the paradoxical effect of attributing poor qualities to the armies and the leaders of the day. The medieval army has been misunderstood and underestimated.

The same was not true of the costly and ubiquitous castles that dotted (and still dot) the landscape of Europe. The importance of the castle in European history, and not just military history, is impossible to overstate. The castle functioned as noble or royal residence, seat of government, defensive fortification, base of offensive operations, place of refuge, and tool of oppression. We know of no global calculation of the cost of castle building to European society as a whole, or even if such is possible. What we can do is consider the expenses that rulers poured into their construction, funds that then were unavailable for raising armies. The most powerful rulers could, of course, afford to build castles and raise armies, but funding one inevitably reduced funding for the other. The results were not trivial. Heavy spending on castles in some cases eliminated the opportunity for offensive warfare, the spender relying on the defensive strength of his fortifications to wear an enemy down. In extreme cases the spending bankrupted rulers. Yet the castle was not necessarily a bad investment. Seizing one by force was difficult, dangerous, and time-consuming, and even the introduction of gunpowder did not immediately render them obsolete.

Eventually, of course, gunpowder’s effect was dramatic. Tall vertical walls became targets instead of obstacles. During the expulsion of the English from France after 1450, heavy artillery could topple walls “in a matter of hours.” And the cost of fortifications designed to blunt cannon shot, such as the trace italienne, were “enormous. Only the wealthiest states and cities could afford the scores of cannon and the enormous labor of construction.” All this took place, however, after the centuries studied here. In fact, well after; although the first gun was introduced in Europe in 1326, it was a century before guns overtook catapults in effectiveness.

Gunpowder, however, only accelerated a trend well under way, namely, the centralization of government linked to the growing expense and scale of warfare. Paralleled by the growth of cities, monarchies steadily acquired power at the expense of the nobility. In Italy, for example, city-states retained their independence even past the Renaissance in some cases. Some German cities were not amalgamated into larger units until the time of Napoleon. The military result of the growth of cities in the Middle Ages is complex. Individual nobles could not besiege fortified towns but neither was aristocratic control over the countryside seriously threatened. Eventually, the small yielded to the great as the larger states accumulated capital, war expanded in scale and cost, and the great powers could “milk their economies” to pay for war.

The period under examination, AD 1000–1300, is a reasonably well-defined period in military history. Warfare was different from preceding and succeeding periods. The period can safely be called the Age of the Castle. Stone fortifications became common. By the end of the thirteenth century development of the castle was essentially at an impasse. No major design advances were made in the fourteenth or fifteenth century. Whether this was due to the changing nature of warfare or because design possibilities had been exhausted is beyond our scope here. Suffice it to restate that the typical ruler of the Middle Ages often chose to build castles despite thereby foregoing the only other pertinent military option—hiring an army. Choosing to build castles cost the opportunity to build armies.

Studying the economics of castles and warfare can also tell us a lot about the time. It is a truism to describe a period as “complex” or “controversial,” but it is hard to think of one that deserves these terms more than the Middle Ages. Information is fragmentary and the numbers often literally do not add up. There was no well defined central government. Even the most popular term used to describe life—feudalism—creates arguments. Some historians refuse to use the word at all. Others disagree about what the “system” of that age really meant. Was it, for example, “government by contract” (as opposed to public law) or was it merely the legitimization of the power of violent groups who dominated the land and turned their raw power into tradition and principle that all had to obey? Those who have the capacity for organized violence, the argument goes, have the most rational self-interest to organize government. Among small groups peaceful agreement is more likely because everyone can see the benefits of collective security, but in larger entities the individual cannot see the benefits very clearly, just the cost, and may be less likely to agree voluntarily to pay for castles, weapons, and sundries. If true, this argument could help explain the frequency of civil wars in the age.

The huge sums that medieval rulers spent on war (indeed, they seemed to spend on little else) mean that every aspect of war had major effects on economic trends, and vice versa. Improved taxation (“improved” from the ruler’s perspective, of course) made military spending possible, and war required much of this sort of improvement. In the tenth or eleventh century a landholder might generate enough income to build a simple motte and bailey castle—consisting of an earthen mound, a circular wall or walls, and, in the center, a fortified tower as a final place for retreat—but revenues from estates could not keep pace with the growing costs of war. As landholdings of monarchs became less important, rulers became quite creative. The English kings exploited archaic land taxes, managed vacant bishoprics, pocketed profits from minting, collected every conceivable feudal due, taxed the laity for the crusades, and laid the foundation for the shift to universal taxation. This pattern—modernization of taxation due to war—can be seen in France and Spain as well. In France, the ordinary revenues grew from 86,000 to 400,000 livres tournois between 1180 and 1290, supplemented by a variety of special levies to fund wars and crusades. The Spanish monarchy achieved similar results, further stretching its money through devaluation. Monarchies grew in power as well as wealth. Only in the Holy Roman Empire did the pattern not occur, because the imperial “government” lacked the means to compel payment.

Monarchs were thus able to acquire the funds for castles and armies and make war the province of the mighty alone. Ordinary nobles could not keep up. But it took time. Medieval European monarchs had few legal powers to tax and their organizations and institutions were too weak or disorganized to keep the flow of money steady. Payments in lieu of service were common, but these were so hard to keep track of that they disappeared in the fourteenth century. The creativity of royal treasurers was boundless, however. They chartered towns for a fee, took over church properties, used requisitions, paid for supplies with means other than cash, inflated the currency, borrowed money, and imposed public loans. Yet it was never enough. Warfare consumed the treasures of state.

The chapter proceeds as follows. First we examine the concept of opportunity cost with respect to castle-based warfare. Next we present an accounting for the sheer number of castles, especially in relation to English kings. Then we assess the cost of castle building and show why, despite the truly enormous cost, the advantages outweighed the cost. Armies were not irrelevant but their cost was high and the advantages slight. Finally we point to where economic principles other than the principle of opportunity cost may be seen in the history of castle building.

Opportunity Cost and Warfare

Opportunity cost is a fundamental principle of economics. This cost refers not to what one pays for a purchase, but rather to the highest-valued alternative purchase one could have made. For example, reading this chapter now implies foregoing the opportunity of doing something else with your time—such as reading something else, cooking, cleaning, working for money, enjoying one’s family, or just savoring a quiet moment. Anything you do involves giving up the opportunity of doing something else. That is the opportunity cost.

The principle of opportunity cost is at once easy to understand and difficult to apply, in part because the values assigned to alternative courses of action vary from person to person. As regards war, opportunity cost can be applied at several levels. The level considered here involves spending decisions although relative scarcity of resources is not the whole story. In the twentieth century the capacity of governments to support war has increased immensely, but changing technology has made the choice process more difficult. First, decisions have had to be made about which weapon system to purchase. This has created controversy inside the military and outside. Different branches of the service compete for funds, and the competition does not always remain in-house. Major projects attract outside attention, and support may wax and wane. The United States’ B-1 bomber, for example, was authorized by the Nixon-Ford administration, canceled by Carter, and then reauthorized by Reagan. Second, technological change generates ever increasing potential costs. Of course bigger projects have always cost more money, but now the capacities as well as the brute power of weapons have changed. The military airplane’s capabilities and costs have risen so rapidly that a calculation once foretold the one-airplane air force, a machine so monstrously expensive as to swallow the whole of the procurement budget. Pursuing this avenue costs the opportunity to prosecute any realistic scenario of war.

Another level at which the principle of opportunity cost can be applied to warfare is in the arena of operations. A unit sent north cannot simultaneously go south. Reserves deployed to one zone to stop an attack are unavailable to stop one elsewhere. Military leaders attempt to avoid or at least mitigate this conundrum, for example, by deferring definitive deployment until the last possible moment. Eventually a choice is still made, of course, but battles are often won by one side keeping a strong reserve available until the decisive moment. Another way is to place the adversary in an untenable position, for instance, by maneuvering so that the enemy does not know which choice is going to be made, until it is too late. Improved mobility is also a way of moderating the opportunity cost problem as mobility further postpones the finality of the choice. But a choice must be made, and the next-best option must be given up. Thus, an opportunity cost always exists. The only question is just how valuable is the option given up. To be sure, opportunity costs can be low: slow moving, low quality forces can be “used up” without incurring high-valued foregone opportunities, at least from the perspective of the commanders, if not from that of the affected soldiers.

All this only scratches the analytical surface. Many other applications of the principle of opportunity cost to war can be considered. The very decision to go to war is perhaps the most important. The opportunity to fight different types of war should be considered, as indeed the opportunity to choose nonwar options of waging, or resolving, conflict. Then there are the different opportunity costs for different “choosers” in a military system. For ruler, supreme commander, subordinate military leaders, and the rank and file, an aggressive—or any other—military strategy involves different opportunity costs. The potential complexity of the application of this seemingly simple principle is virtually limitless.

Even restricting the application of the principle of opportunity cost to just one facet, such as castle building in the High Middle Ages, involves many difficulties. Taxation, budgeting, and spending in the Middle Ages can only be described as haphazard, or at least they appear so because of the paucity of records.

This quotation, from a standard work on the military history of the age, reveals some frustration of the study of the period. Fortunately, progress has been made, and even as debate regarding the exact numbers will continue, a number of deductions can be made about the labor and capital cost necessary to construct medieval fortifications. About the overall cost there is little dispute. Medieval rulers had the greatest difficulties in paying for their wars, and powerful monarchs had no less trouble despite initially starting with more. “All were driven to desperate expedients to make ends meet.” Worse, possession of more power and territory gave one more to defend. Castles and troops were both necessary, and this led to every conceivable way being devised to raise money. “Since the time of Cicero and Tacitus to the fifteenth century and beyond, authors often asserted that the tranquility of nations was impossible without armies, armies without soldiers’ wages, or wages without tribute.”

The result of the search for funds has been described as “less a system of taxation than a system of plunder,” and this was no metaphor. In England, for example, goods were sometimes seized from merchants and only released after “tax” was paid. And it was never enough. Despite the most vigorous tax collections England had ever known, Edward I (r. 1272¼–1307) constantly outran his financial resources. Between 1294 and 1297 wars with Scotland, France, and Wales required such heavy war levies that laity and clergy alike rebelled, leading to a major constitutional crisis. This was not the result of mere royal greed; bad policy is another matter. In Edward’s last years, the Wardrobe, as the department that paid the army’s bills was called, rarely had a thousand pounds at any given moment, while earlier in his reign it had been able to send its paymasters sums as large as £5,000 at once.

Credit was no permanent solution. Since the twelfth century credit had been steadily expanding across Europe. Tempted, Edward I took two steps: he borrowed, usually from Italian bankers, and he did not repay them, at least not completely. His first bankers, the Riccardi, failed to collect some £18,924; the Frescobaldi firm was shorted some £25,000. It did little good. At his death, Edward I left a debt of some £200,000, almost four times the entire annual royal revenue. Justly, some of this could be attributed to the policies of a king who not only made war constantly but pursued policies almost guaranteed to lead to further wars. Unsurprisingly, periods of peace led to dramatic improvements in the condition of the treasury. But there was more to the matter than the behavior of an overly, and overtly, aggressive king. Far more interesting about Edward I is that, despite running repeated campaigns in France, Wales, and Scotland, he nevertheless chose to plow fortunes into the building of castles.

The Ubiquity of Castles

Given the limits to tax collections, the calls on the purse for recruiting armies and waging campaigns, and the enormous cost of castle building, the number of castles in Europe is nothing but spectacular. Some authorities place the peak of castle building around the beginning of the millennium; others note the immense amount of construction in the twelfth and thirteenth centuries. The difference is partly a matter of archaeological interpretation because many left no surface trace other than the remnants of a mound. But no one who has studied them has come away unimpressed by the numbers involved. A recent survey of a 94-square-mile area (about 243 km²) of Normandy counted four stone castles and twenty-eight earth mounds, remnants of fortifications.

It is important to appreciate that the castle was not merely the tool of a lord fearful of being attacked. Conquerors used them as well. Fulk Nerra (972–1040), one of France’s most famous conquerors and dynasty builders, may have constructed the nation’s first stone castle at Langeais and built fortifications across his domain. William the Conqueror arrived in England in 1066 with a prefabricated wooden castle, and, after defeating the Saxons, sprinkled forts across his new land. As many as five hundred may have been built by the time of his death in 1087. The centrality of the castle in warfare can also be demonstrated by reference to the building of “countercastles,” fortifications constructed by besiegers. This technique occurred at places as widely separated as England and Italy and was employed by William the Conqueror, among many others.

In the Dark Ages, castles consisted of basic timber and earth construction. In the tenth century, there appeared the motte and bailey castle, a central fortified tower placed on an earthen mound surrounded by a circular wall or walls. Militarily useful, these castles were simple to build but were eclipsed by the arrival of the stone castle in the eleventh century, although one may have been built in France a century earlier. Architects and masons now supervised building projects that lasted years and, occasionally, decades.

The result was a costly fortress, essentially impervious to the military machinery of the day. Rulers and nobles now had a residence that could protect them and serve as a base of operations. The political results were decidedly mixed. While kings invariably built castles and used them to tighten their grip on the countryside—“a good fortress was the medieval ruler’s best friend”—they were not throwing up these structures randomly. “The defence systems which they designed, or which developed in the course of centuries are a remarkable expression of their military ideas.” The downside was that this carpet of castles was a magnificent entity with which to resist central rule. Independent nobles as well as castellans, appointed to manage castles for the ruler, became increasingly powerful behind their stone walls. The effect on the countryside can well be imagined. Taxation for castle construction was heavy. Labor was sometimes conscripted for the building works. A castle’s garrison could protect local villages, but it could also threaten them. William of Malmesbury wrote in 1140 that “there were many castles throughout England, each defending their neighborhood, but, more properly speaking, laying it waste.” Small wonder that “to the medieval mind, the castle was the most intimidating force on earth next to the wrath of God, and with good reason.”

The Cost of Castling

Building castles benefited rulers by intimidating enemies and friends, merchants and peasants, nobles and commoners, and especially taxpayers. To determine how much it cost rulers, we need to know how the cost of castling compared with the cost of recruiting an army. The cost lay mostly in direct labor cost, as most labor had to be paid. (In contrast, raw material cost does not seem to have been much of an issue.) In addition to this explicit outlay, there was also the opportunity cost of labor; for example, masons working on castles could not be employed elsewhere. The garrison cost of castles was not a major consideration as the number of soldiers needed to defend a well constructed castle was surprisingly small. The most important cost issue with garrisons was their reliability. An unreliable noble appointed as castellan now possessed a powerful tool with which to defy his mentor. As castellans often caused trouble, this was by no means a trivial issue, and rulers definitely considered it a significant matter.

The actual cash outlay for building substantial castles eventually exceeded the resources of many nobles and stretched those of even the most powerful kings. The English king Richard I, the “Lionheart” (r. 1189–1199), needed to construct a fortification that would protect Normandy from invasion and serve as a base for further operations at the expense of the French. In only two years, his laborers constructed Château Galliard, one of the twelfth century’s most spectacular castles. The £11,500 spent there far exceeded the £7,000 he spent on all his other castles put together and was more than he spent fortifying an entire town like Dover. As his revenues for those two years amounted to about £39,500 pounds, Château Galliard cost him almost 30 percent of his income. In two of his ten years at the helm, his income was less than the cost of the château.

Galliard was but one castle. The broader case can be seen in the works built by Edward I during his conquest of Wales. A powerful monarch who fought with success against the Welsh, Scots, and French, he enjoyed tremendous tax revenues by the standards of the age. It would not prove enough, although castle building alone did not break his bank. He embarked on eight projects in Wales: Aberystwyth, Caernarfon, Conwy, Flint, Rhuddlan, Builth, Harlech, and Beaumaris. All but the last three were integrated with fortified towns. Considerable data survive about the total cost of these castles, although the numbers are conservative. The clerk in charge of each castle’s budget did not pay every associated expense. For example, the substantial wages that workers were paid while traveling from home to the works were paid by each sending shire. While this expense did not come out of the king’s pocket, it certainly did come from the country’s and thus counts as a cost of castle building.

Estimated costs for Edward I’s Welsh castles are given in table 2.1. The variations in the total obtain because for some years only estimates can be made. Not only did repairs have to be made after Welsh attacks, castles were frequently modified years after the original building had begun. As noted, the calculations are conservative. But no authority places the cost of the Welsh castles under £80,000, and several place it closer to £100,000, “an outlay such as a modern government might devote to building a fleet of nuclear submarines.”

Edward I’s annual income over twenty-five years ranged from less than £25,000 to over £100,000, with an average, including a variety of special taxes and parliamentary subsidies, of around £67,500. Unfortunately for Edward, not to mention the taxpayers, the fortifications outran his finances. Caernarfon, the most spectacular site, never was completely finished inside. “In Wales, Edward’s great castle at Beaumaris remained unfinished, a striking witness to his financial problems.” The castle’s walls only reached half their intended height. The treasury could no longer pay the wages of the work crews at Beaumaris. Even heavy levies in Ireland could not make up the difference. As parliament’s great magnates became unexcited about disgorging endless funds for war, a constitutional crisis resulted. No British monarch would ever attempt castle building on this scale again. Perhaps later rulers, or their advisors, were all too aware of the crisis that occurred in 1296–1297. Although not the sole cause, the magnificent walls of Wales perhaps were the single biggest factor:

The nobles’ love of the king’s masonry was doubtless tempered by their awareness that projects on this scale were no longer within their own grasp. A handful of nonroyals in England and on the Continent could afford big walls. Gilbert de Clare built the enormous castle at Caerphilly. In France, the counts of Champagne bought castles from financially strapped nobles. Of two hundred English baronies in the twelfth century, only 35 percent had castles, others making do with fortified houses. Between 1154 and 1214 the number of baronial castles actually fell, from 225 to 179, while royal fortresses more than doubled in number, from 45 to 93. In an age when royal income never fell below £10,000, only seven barons were earning more than £400, the average was about £200, and at least twenty had incomes of less than £20. An up-to-date castle at the end of the twelfth century cost about £1,000 although a basic stone castle could be built for £350.

The nobles were at a disadvantage in the castle arms race with regard to both money and legal powers. The king had the greater ability to pay and also the greater ability to make people fulfill his wishes. The king could force a shire to cover significant military expense. The nobles were in a relatively poor position. While the king had begun in England, as elsewhere, as a primus inter pares, he was now very much primus. Yet as Edward discovered during the crisis of 1296–1297, he was definitely not free of fiscal constraints and hence remained somewhat dependent on the wishes of his nobles.

New weapons often increase the capability of the individual soldier, but this can be offset by growing development and construction (or manufacturing) costs. In this respect, the stone castle was fairly typical. The number of soldiers needed to defend it might be small, but the number of people needed to build it was quite large. In the days of the motte and bailey castle, the labor required for building a very basic fort was small. A hundred men working for a month could build a modest one, and if they labored about three months, a substantial mound could be constructed. The stone castle was another matter. The tower constructed at Langeais required about 83,000 “average work days” to construct, ten times what a substantial motte and bailey needed. Langeais was built in two seasons. If the workforce was able to labor six months each year, there would have had to be some three hundred laborers continuously on site. The labor of an additional 1,000 to 1,200 farmworkers would have been needed to sustain the builders.

Figure 2.1. Edwardian castle design
This shows a “typical” Edwardian castle with some of the features that made it so expensive. These included (1) multiple walls; (2) numerous towers; (3) concentric circles of masonry required to give strength to walls and towers; (4) the use of round, rather than square, towers; (5) extensive interiors, as the castles were intended as royal residences; (6) water access; (7) multiple gate houses; and (8) difficult locations, such as hilltops. Addititional architectural factors in the high cost included size, height of walls, depth of foundations, and overall complexity.
Ilusstration by Debra van Tuyll

Edward I’s castles required much more (fig. 2.1). None of his fortifications were completed in less than five building seasons (six to seven months each), and three took much longer. Many of the works were done at the same time. After 1277, Builth, Aberystwyth, Flint, and Rhuddlan were being built at the same time; after 1283, Conwy, Caernarfon, and Harlech were going up together. The number of workers at each castle varied enormously. At Builth only a hundred might be present at any one time, but at Beaumaris the total exceeded 3,000. In 1283–1284, about 4,000 men were employed at Conwy, Caernarfon, and Harlech, while 3,500 were hired in 1295 to work on Beaumaris and repair Caernarfon (which was damaged in an uprising). The population in Edward I’s day was about three to four million people, so that the use of 4,000 workers was not a negligible number (an equivalent number of Americans today would be about 300,000). Workers had to be brought in from faraway shires. “In other words, we seem to be driven to the conclusion that the numbers of workmen employed by Edward I on his Welsh castles were sufficiently great to constitute a noticeable draught upon the total pool of mobile labour that was available in the England of his day.” That, of course, was the rub. With much of the population engaged in subsistence agriculture, the pool of labor on which to draw was not massive. Designers and masons were hired from the Continent. This reduced the labor drain in England (although at a financial cost) yet the castle-building program may, nevertheless, have absorbed a tenth of the national workforce. The impact was greater than army recruitment would have been. “The recruitment of men for the army may have had similar effects on occasion, but probably more serious was the call for skilled workmen to build the great Welsh castles, which must have had its effect on the building industry.” While that conclusion cannot be accepted in its entirety—church construction may have contributed to a surplus of available stone masons—the burden was still huge. The true experts in the business, the architects and designers who knew the military ins and outs of castles, were greatly valued and greatly compensated, excepting the unfortunate architect of Ivry (France) who was put to death so that he could not reveal its secrets.

Building a castle was only a first step. Castles had to be adapted, modified, improved, or even replaced if they became obsolete. Improvements in siege warfare required design changes. The square stone keep was sufficiently expensive that Norman castle-owners sought simply to reinforce their motte and bailey castles to hold costs down. Increasing costs of fortifications drove increases in military expenditure throughout the eleventh century. The crusaders further stimulated the process by bringing back innovations from the Middle East. The motte and bailey castles mutated from inexpensive palisaded hills to costly stone fortifications as powerful concentric walls replaced the palisade. The outer “curtain wall” became more sophisticated in the twelfth and thirteenth centuries as towers were added for flank fire. By the time castle building reached its peak toward the end of the thirteenth century, the two-wall system, with a “killing ground” in between, had become a standard design. This did nothing to constrain the continuing expansion of costs. There was increasingly no limit on how much could be spent, how many improvements made, and how many refinements introduced.

Another cost, harder to calculate, was that the castle suffered from inherent weaknesses. No castle could hold out forever. Even Galliard, perhaps the most expensive castle of the twelfth century, fell to the French. No defense is impregnable. “The best that a besieged castle could hope for was to raise the price of victory to a point which the besiegers would be unwilling to pay.” That price could be exacted in various ways. Storming a castle was one of the most dangerous activities any medieval fighter could undertake because repelling such an attack was exactly what the stone walls were designed for. A besieging army often suffered more than the besieged from lack of shelter, the spread of disease, periodic food shortages, and the threat of a relief force appearing in the rear. Once feudal service requirements expired, the besieging troops would have to be paid, making long sieges unlikely.

Regarding pay and length of service, the castellan had two advantages. Garrisons tended to be small. Admittedly, their numbers, like those of armies, are hard to calculate because medieval chroniclers were notoriously bad with numbers. Nevertheless, it is rare to find evidence of large garrisons, and sometimes these were raided to flesh out field armies. A second advantage was that the soldiers in a surrounded keep could hardly leave, and no pleasant result could ensue from stopping fighting, unless the garrison in its entirety decided that its obligation to serve had expired, which occasionally did happen. Yet the maintenance of garrisons also presented many problems. Defending a castle was not a task for amateurs. Professionals had to be hired. Because many of these were essentially mercenaries, their loyalty was sometimes doubtful and mutiny was a serious risk. Gatehouses were constructed to provide a safe place for the castellan to live and also to allow him to control entry and exit. But the loyalty of the castellan was also a problem for rulers. Moreover, the paid or “stipendiary” troops had to be convinced that their ultimate lord was loyal to them. If they were besieged and their lord made no effort to relieve them, they might surrender as they then “had no natural lord.”

Even if the cost of garrisoning castles were overcome, inherent weaknesses remained. A castle can do little to prevent an attacker from choosing his moment. “No matter how strong, an isolated castle was vulnerable . . . A network of castles supported by a field army was a very different proposition, but only a few kings could afford such a combination.” Improved construction techniques could make the siege longer and more difficult, but not impossible. The early motte and bailey castle was highly vulnerable because the various parts of the defense could not support each other. That was solved by the more modern stone castles, but the impregnable fort was never built. Galliard was considered so, but it fell five years after its completion. Its fall illustrated a major conundrum for the builders. A well designed castle could deter an attack but not if its location was truly vital. Then the attacker would find a way. Any castle would eventually succumb to starvation.

That a castle could be taken was perhaps no more significant than that a field army could be beaten. More significant to evaluating the opportunity cost of choosing a castle over an army is that a castle cannot maneuver. In fighting Edward I, the Welsh frequently bypassed the king’s castles, attacking them only when they chose. In turn, Edward did not spend more than ten days besieging Welsh castles. The English did construct castles during the conquest of Ireland but these merely became targets for successful destruction raids by the Irish. Spreading castles over the countryside during a conquest sometimes created more resistance than it could contain. The most expensive fortifications simply could not fulfill the strategic functions assigned them. Historian Michael Prestwich judged Edward I’s castles to be “the most magnificent series of fortifications to be built in all of Medieval Europe,” even as he questioned the wisdom of Edward’s strategy regarding the resources required to maintain them. If castles were stupendously expensive, ultimately vulnerable, and prevented the build-up of field armies (the main opportunity cost), why build them? The advantages must have been thought more than enough to offset these drawbacks.

The Advantages of Castles

Historiography of medieval warfare has dispelled the notion that commanders and rulers were simpletons. Medieval rulers were keenly aware of their choices and attending costs. Knowing the cost of castles, they continued to build them. Even when short of money, they continued to build them, risking confrontation with vassals and taxpayers over the bill. To leaders of the age, the benefit of permanent walls outweighed the cost.

This was based on a very important consideration: the multiplicity of goals met by building castles. The castle was anything but a stone ring within which to hide from conflict. The castle dominated the landscape, figuratively and literally.

This multiplicity of roles helps explain why castles were the “main bones of contention . . . and focal points” of struggles. As a center of government and war in a warlike age, the castle was a symbol. The great royal castles of Wales were more than Edward I’s way of controlling the Welsh; they were a way of reminding the Welsh that he was there. Evidence suggests that Edward understood this perfectly well. External architecture was used as a means of impressing the people, such as at Caernarfon. Its expense was magnified by its unique construction: Edward intended its walls to look like Constantinople’s. Good locations were exploited without regard to expense, such as at Conwy, where the castle overlooks most of the town. In especially vulnerable locations, such as Beaumaris, on remote Anglesey, Edward’s engineers incorporated every possible feature—double walls, moat, access to the ocean, a profusion of towers—that could add to its strength. Construction of Edward’s castles frequently included huge round towers that were doubly advantageous because they were harder to assault and gave the castle an especially imposing visage. This method of building was expensive because for structural reasons the walls consisted of multiple layers of materials, as erosion and age now reveal. The appearance of the castles was more than a matter of aesthetics or ego. As is shown by the elaborate and complicated interiors, these buildings were also the residences of high officials—and sometimes the monarch himself. The castle was wasted expense if it were mere vanity, but sensible expenditure if viewed from the perspective of occupation politics.

For the expansion-minded magnate the castle was the best, perhaps only, means of laying permanent claim to disputed, threatened, or rebellious land. “The great value of the castle was that it held down the land; without taking it there could be no secure mastery of the land that it dominated.” Controlling territory required removing your rival’s castles, as well as having your own castles there. This strategy can be seen in action in Germany, France, and Britain. In Germany, the Duke of Swabia advanced down the Rhine, building one castle after the other, using each one to subjugate the country before continuing to the next spot. Fulk Nerra laid the basis of the Angevin dynasty in France by building substantial castles across his territories, spacing them so that mounted forces could easily move from one to the other. Edward I’s needs were slightly different from Fulk’s as he had to contend with entire hostile populations but his techniques were, nevertheless, similar. Each Welsh castle was built no more than a day’s march from its nearest neighbor, and they were also located where they could be easily supplied. Although the criticisms of the amounts spent seem just, the revolutionary spirit in Wales has led one author to conclude that a “policy of energetic castle-building was essential.” Perhaps it is no accident that Edward kept Wales but lost Scotland, where he did not engage in much building. His strategy there has been described as “less impressive, consisting as it did of sending northwards large armies with the goal of bringing the Scots to battle.”

The Welsh were not the only medieval Europeans to look askance at the forbidding fortresses in their midst. The temptation to use the castle’s advantage to abuse surrounding inhabitants was too great. According to the Anglo-Saxon Chronicle, early medieval castles were used to imprison and torture people who might have goods. The Normans were long thought to have gained supremacy in parts of the Mediterranean because of the supremacy of their mounted warriors, but it now appears that their most successful strategy was to take a castle and use it as a base from which to terrorize the surrounding district into submission. When Alfonso VI captured Toledo in 1085, he placed a garrison at Aledo, far to the south of his effective rule, where it functioned as “a thorn in Muslim flesh” until 1092.

Normans, Anglo-Saxons, Anglo-Normans, and Spaniards were able to maintain castles for years among hostile peoples. A field army could hardly have done so. It might be a better instrument for short-term conquest, but permanent occupation was another matter. An army could rescue a besieged castle, but a castle could shelter a small army. In an age where capacity to stay in the field was limited, this gave the castle a crucial advantage. The historical literature is filled with examples of medieval commanders avoiding battles, and some never fought any at all. With a castle as a handy retreat, there was no need to fight unless victory was certain, in which case the adversary would not fight. Clausewitz’s dictum that “no battle can take place unless by mutual consent” is unusually accurate for this age. Most invaders used a single line of advance and could easily be evaded. When Edward III (r. 1327–1377) invaded Scotland, the Scots either avoided battle or took up strong defensive positions the king was unwilling to assault. Even when multiple lines of advance made complete avoidance impossible, the weaker force could retreat into its castles and wait for the fighting season to end. Fulk Nerra avoided battle whenever possible. Even when it was not clear that the enemy was stronger, fighting from behind walls was tempting.

Fighting from behind walls deterred direct assault, and this might tempt us to think of this kind of war as “low cost.” It was not. The suffering among ordinary folk was magnified in two ways. Obviously a successful storming was followed by massive misdeeds. More often, it lengthened the war. According to J. F. Verbruggen, the lawyer and pamphleteer Pierre Dubois

Longer wars spelled higher tax bills, more frequent military service, more raids, property seizures, burning of hovels and possessions, and the privations of being besieged, even if the result was not a storming or a subsequent slaughter. In fact, a type of conflict developed that was relatively low in direct military cost but devastating for the populace. Feuding, as it was called, involved plunder, looting, and devastation; in other words, warfare aimed directly at civilians. Absent a carelessly opened gate, the castle was immune to these attacks. It could, however, serve as a place to store the loot.

Retreating behind walls might also imply that a cost of reliance on castles was the sacrificing of offensive strategy. Again, this was not quite true. Yes, castle spending inevitably meant less money for the field troops. But defending a castle was not quite the same as defensive warfare. A castle could have both offensive and defensive purposes, and very few castle builders thought solely in terms of defense. From the moment of their construction, castles “threatened neighbors, and . . . often served as bases for attack”; they “could menace enemies as well as protect friends.” Rarely was the defense of a castle a passive operation. “The overriding thought in castle strategy was not passive defence but action and destruction.” Moving across the drawbridge actually strengthened the “retreating” force. “Shutting oneself up in a castle was not an attempt to avoid conflict, but a manouevre to make the enemy fight at a disadvantage. . . . The defence had an enormous advantage. To an invader time would be vital.” Depending on distance, essentially three cases existed in which the castle garrison threatened an enemy. First, sallies might be made against the immediate besiegers. Second, raids from the castle could threaten areas within a day’s round trip or so. An example of this can be seen in the castle at Le Puiset, taken by Louis VI in 1111; no one dared to come within 8–10 miles of the walls. And third, the castle’s troops could be launched on a major operation against a neighboring principality. It is no coincidence that the most offensive-minded leaders of the age often withdrew behind stone walls. The castle was not purely defensive.

Raids and major operations could be contained by siege. A brief siege would be meaningless, as the castle’s troops could return to their offensive ways as soon as it ended. To contain an aggressive prince, it follows that his garrisons had to be besieged to the point that they would surrender rather than face a worse experience. Siege warfare became the operational center of medieval warfare, not just to overcome the defense but to prevent the fortified enemy from engaging in offense. The castle became the geographic center of warfare. In civil wars the focus on castles was even greater than normal because there was more emphasis on establishing and maintaining control of territory. Even the English campaigns in Scotland revolved around castles. The English capture of Stirling (1304) ended resistance more effectively than the famous Battle of Falkirk (1298), and the English disaster at Bannockburn (1314) was a direct result of the need to relieve the garrison at Stirling. Robert Bruce attempted to make successful sieges more decisive by destroying captured castles but even such extreme “decastelization,” practiced elsewhere as well, still depended on a successful siege to begin with.

If we accept that siege was central to medieval warfare, why its lack of study until the 1990s, especially since the methods and conventions of siege warfare did not change very rapidly? A straightforward answer is that a generation of military historians preferred to emphasize medieval open-field battle. Historians were nearly as affected as people at large by the image of the heroic knight on horseback. The armored cavalry of the High Middle Ages can hardly be disregarded, of course, but it played no role in siege warfare. A knight could fight for or against a castle, but hardly while horsed. He could climb ladders, fire weapons, pour boiling oil, or give orders to so do, but this fighting, while often more dangerous than the charge with lance and sword, would produce much less epic poetry. The horse in such operations was rarely a gallant, elegant steed, but rather the sturdy and ugly draft horse that pulled the battering rams and other heavy equipment. Sometimes that work was given to the even less glamorous ox.

Glamorous or not, medieval warfare required sieges. The only alternative was rapid raiding, so rapid that counterattacks by castle troops were irrelevant. This was unlikely as the most important points on the map were the most likely to be occupied by a castle. Sieges, while difficult and expensive, were inevitable.

This seems to have been the case throughout the Middle Ages. Castles might be primitive, but taking them was often beyond “the incoherent and ad hoc armies of Western Europe.” Even the simple motte and bailey castle was rarely captured. A documentary and archeological study of some one hundred and fifty such castles in Belgium has found scarce references or evidence of successful attacks. Only five are definitely known, although the baileys were sometimes burned, and one castle was captured by two knights and twenty peasants when the gate was left open.

The single stone keep or donjon also posed extraordinary problems. The donjon of Coucy (built 1223–1230) was so strong that its barons defied royal commands for two centuries! That these castles were smaller than the motte and bailey variety was no balm for putative conquerors. “Long passive sieges were usually futile, because the small garrisons required to defend these keeps used up their vast stores very slowly and used little water.” Even large castles, if properly designed, could be defended by small groups. Caernarfon survived two sieges (1403–1404) and inflicted three hundred casualties even though its garrison was down to twenty-eight men. In 1216 a substantial French army required fifteen days to capture a castle held by thirteen men; Harlech resisted the rebellion of 1294–1295 with a garrison of only twenty. The famous crusader castle Krak des Chevaliers, defended by a skeleton garrison, survived twelve assaults and was finally taken only by ruse in 1271. Château Galliard had more troops—one hundred and forty at the time of its surrender—and was only lost after a six-month siege, a five-week assault, an inadvertent failure to defend a window, which allowed the attackers in, and no serious relief attempt. For the attacker, the situation did not improve over time. “By 1300, the odds of a strong force successfully forcing a well-built and well-defended fortress were less than they had been three centuries earlier.” Gunpowder changed things, of course, but seven seventeenth-century cannon could not reduce the twelfth-century keep at Rochester.

The attacker faced severe costs. Money supplies sometimes succumbed before the defense did. Stephen (r. 1135–1154) spent £10,000 besieging Exeter Castle, a sum five times his estimated annual income. Indeed, a successful siege could be financially disastrous. Henry III (r. 1216–1272) captured Kenilworth in 1266 through negotiation, “but the siege had been cripplingly expensive, absorbing the income of ten English counties.” The personnel cost constituted the real culprit. On both sides specialists were needed. A long siege quickly raised expenses because feudal levies could only be required to serve for periods set by tradition and law, and once these were exhausted, they had to be paid. The cost of personnel—to ruler and soldier—was high. Estimates of the numbers needed for a successful storming range from 4:1 to 10:1, and this seems conservative in view of some castles’ successful defense against odds of 50:1. For the soldier, the attack was extremely hazardous and even after a breach of the wall it was not always easy to get troops to assault, sometimes requiring leading nobles and rulers to lead from the front. This could easily backfire. In 1088 a king was leading an attack on a gate when a woman described as “female in sex but not in spirit” threw a millstone on his head, bringing his reign to a premature end.

Consequently, the attackers often opted for the slow process. But time itself was a cost. The besieging army could do nothing else and decisive victory could prove elusive. Stephen attacked rebellious baronial castles one by one, capturing a number through starvation, but at his death much of his kingdom was still in rebel hands. Delays could result in failure and the collapse of morale. To such psychological problems the garrison troops were vulnerable as well, but their mighty blocks of masonry were not. In a word, the nub of the problem was that the resources invested by an attacker were much greater than those of the defender.

The result was an endurance contest that often ended without a decisive fight. No definitive numbers exist for successful versus unsuccessful sieges. That the failure rate was very high is undisputed; indeed, the majority of successes were the result of negotiation, not storming. William the Conqueror allegedly never failed to take a castle, but he did so mostly by agreement. Even after a three-year siege of a castle in Normandy, the famous duke offered terms because he “had been forced to recognize that taking the castle was too demanding in time and resources.” And this medieval ruler, more than most of his contemporaries, was able to assemble and maintain the obvious alternative to the castle, a trained and reliable field army.

Whether the castle could have survived much longer once gunpowder became prevalent is actually a moot point. Its very strength was a barrier to the growth of great national governments. Monarchs regarded private castles as an inherent threat. Legal and other measures were taken to eliminate them. In Britain, the Tudors were particularly effective in eliminating great noble castles as part of a well designed program to establish the state’s monopoly on violence. In France, Louis XIII probably destroyed more castles than he built. This trend was actually a paean to the military virtues of the castle.

An excerpt from

Castles, Battles, and Bombs

How Economics Explains Military History

Jurgen Brauer and Hubert van Tuyll

The Case of the Medieval Castle
and the Opportunity Cost of Warfare

Opportunity Cost and Warfare

The Ubiquity of Castles

The Cost of Castling

The Advantages of Castles

See also:

An excerpt from

Castles, Battles, and Bombs

How Economics Explains Military History

Jurgen Brauer and Hubert van Tuyll

The Case of the Medieval Castleand the Opportunity Cost of Warfare

Opportunity Cost and Warfare

The Ubiquity of Castles

The Cost of Castling

The Advantages of Castles

See also:

The Case of the Medieval Castle
and the Opportunity Cost of Warfare