This is the third part of a five part (I, II) series covering some of the basics of fortifications, from city walls to field fortifications, from the ancient world through to the modern period. Last week, we used the Romans as an example to see how the needs of a given fortification changed its structure and design, from marching camps designed to protect armies on the move from sudden assaults to permanent systems of frontier fortifications designed to act as force multipliers, containing and channeling border incursions.
This week we’re going to look at what I am going to call ‘point defenses’ – permanent fortifications that don’t exist as part of a larger fortification system, but which are instead designed to protect a single point, like walled cities or castles (fortified private residences). Now I want to promise here at the beginning: we are actually going to get to the defensive structures and the ‘cool’ stuff like towers and gates and walls and ditches and so on. But first we’re going to have to lay some conceptual groundwork about what exactly a castle is supposed to be doing in order to understand why these fortifications are designed in the way that they are.
Now this is, as you may well imagine, a really large topic and so this post is going to be little more than an overview, even given its impressive-looking read time. Really, if you want to study castles or walled cities in more depth, there really is no substitute to looking individually at examples from a given area and era, especially since most fortifications from this period – especially the larger and more impressive ones – tend to be sui generis to at least some degree. Still I hope that at least an overview will serve to set out some of the basics.
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Frontier fortifications and army bases often make a degree of intuitive sense, either aimed at controlling crossings over an entire border or protecting a military force in the field. Point defenses1 like walled cities or castles (or defensive systems that don’t cover the entirety of a frontier) often make less sense to modern readers and students, invariably leading to the famous misquotation of George S. Patton that, “Fixed fortifications are a monument to the stupidity of man” – what he actually said was “This [the Maginot Line] is a first class case of man’s monument to stupidity,” a comment on a particular set of fortifications rather than a general statement about them and one, it must be noted, made in 1944, four years after those fortifications were taken so we also ought not credit Patton here with any great foresight.
As an aside, the purpose of the Maginot Line was to channel any attack at France through the Low Countries where it could be met head on with the flanks of the French defense anchored on the line to the right and the channel to the left. At this purpose, it succeeded; the failure was that the French army proceeded to lose the battle in the field. It was not the fixed fortifications, but the maneuvering field army which failed in its mission. One can argue that the French under-invested in that field army (though I’d argue the problem was as much doctrine than investment), but you can’t argue that the Maginot Line didn’t accomplish its goals – the problem is that those goals didn’t lead to victory.
So before we get into the design of point defenses, we should talk about what these are for. Generally, fixed point defenses of this sort in the pre-modern world are meant to control the countryside around them (which is where most of the production is). This is typically done through two mechanisms (and most of point defenses will perform both): first by housing the administrative center which organizes production in the surrounding agricultural hinterland (and thus can extract revenue from it) and second by creating a base for a raiding force which can at least effectively prohibit anyone else from efficiently extracting revenue or supplies from the countryside. Consequently if we imagine the extractive apparatus of power as a sort of canvas stretched over the countryside, these fortified administrative centers are the nails that hold that canvas in place; to take and hold the land, you must take and hold the forts.
In the former case, the fortified center contains three interlinked things: the local market (where the sale of agricultural goods and the purchase by farmers of non-agricultural goods can be taxed and controlled), a seat of government that wields some customary power to tax the countryside through either political or religious authority and finally the residences of the large landholders who own that land and thus collect rents on it (and all of these things might also come with significant amounts of moveable wealth and an interest in protecting that too). For a raiding force, the concentration of moveable property (money, valuables, stored agricultural goods) this creates a tempting target, while for a power attempting to conquer the region the settlement conveniently already contains all of the administrative apparatus they need to extract revenue out of the area; if they destroyed such a center, they’d end up having to recreate it just to administer the place effectively.
In the latter case, the presence of a fortified center with even a modest military force makes effective exploitation of the countryside for supplies or revenue by an opposing force almost impossible; it can thus deny the territory to an enemy since pre-industrial agrarian armies have to gather their food locally. We have actually already discussed this function of point defenses before: the presence of a potent raiding force (typically cavalry) within allows the defender to strike at either enemy supply lines (should the fortress by bypassed) or foraging operations (should the army stay in the area without laying siege) functionally forcing the attacker to lay siege and take the fortress in order to exploit the area or move past it.
In both cases, the great advantage of the point defense is that while it can, through its administration and raiding threat, ‘command’ the surrounding hinterland, the defender only needs to defend the core settlement to do that. Of course an attacker unable or unwilling to besiege the core settlement could content themselves with raiding the villages and farms outside of the walls, but such actions don’t accomplish the normal goal of offensive warfare (gaining control of and extracting revenue from the countryside) and peasants are, as we’ve noted, often canny survivors; brief raids tend to have ephemeral effects such that actually achieving lasting damage often requires sustained and substantial effort.2
All of which is to say that even from abstract strategic reasoning, focusing considerable resources on such fortifications is a wise response to the threat of raids or invasion, even before we consider the interests of the people actually living in the fortified point (or close enough to flee to it) who might well place a higher premium on their own safety (and their own stuff!) than an abstract strategic planner would. The only real exception to this were situations when a polity was so powerful that it could be confident in its ability to nearly always win pitched battles and so prohibit any potential enemy from getting to the point of laying siege in the first place. Such periods of dominance are themselves remarkably rare. The Romans might be said to have maintained that level of dominance for a while, but as we’ve seen they didn’t abandon fortifications either.3
So fortifying key centers makes sense. How do you do it? We should start with castles because, we ‘ll see, things are easier when the position being defended is small.
Long on Rooks, Short on Pawns
While fortifications obviously had existed a long time, when we talk about castles, what we really mean is a kind of fortified private residence which also served as a military base. This form of fortification really only becomes prominent (as distinct from older walled towns and cities) in 9th century, in part because the collapse of central authority (due in turn to the fragmentation of the Carolingian Empire) led to local notables fortifying their private residences. This process was, unsurprisingly, particularly rapid and pronounced in the borderlands of the various Carolingian splinter kingdoms (where there were peer threats from the other splinters) and in areas substantially exposed to Scandinavian (read: Viking) raiding. And so functionally, a castle is a fortified house, though of course large castles could encompass many other functions. In particular, the breakdown of central authority meant that these local aristocrats also represented much of the local government and administration, which they ran not through a civil bureaucracy but through their own households and so in consequence their house (broadly construed) was also the local administrative center.4
Now, we can engage here in a bit of a relatable thought experiment: how extensively do your fortify your house (or apartment)? I’ll bet the answer is actually not ‘none’ – chances are your front door locks and your windows are designed to be difficult to open from the outside. But how extensive those protections are vary by a number of factors: homes in high crime areas might be made more resistant (multiple deadbolts, solid exterior doors rather than fancy glass-pane doors, possibly even barred windows at ground level). Lots of neighbors can lower the level of threat for a break-in, as can raw obscurity (as in a house well out into the country). Houses with lots of very valuable things in them might invest in fancy security systems, or at least thief deterring signs announcing fancy security systems. And of course the owner’s ability to actually afford more security is a factor. In short, home defenses respond to local conditions aiming not for absolute security, but for a balance of security and cost: in safe places, home owners ‘consume’ that security by investing less heavily in it, while homeowners who feel less safety invest more in achieving that balance, in as much as their resources allow. And so the amount of security for a house is not a universal standard but a complicated function of the local danger, the resources available and the individual home owner’s risk tolerance. Crucially, almost no one aims for absolute home security.
And I go through this thought process because in their own way the same concerns dictate how castles – or indeed, any fortification – is constructed, albeit of course a fortified house that aims to hold off small armies rather than thieves is going to have quite a bit more in the way of defenses than your average house. No fortification is ever designed to be absolutely impenetrable (or perhaps most correctly put, no wise fortress designer ever aims at absolute impenetrability; surely some foolish ones have tried). This is a fundamental mistake in assessing fortifications that gets made very often: concluding that because no fortification can be built to withstand every assault, that fortification itself is useless; but withstanding every assault is not the goal. The goal is not to absolutely prohibit every attack but merely to raise the cost of an attack above either a potential enemy’s willingness to invest (so they don’t bother) or above their ability to afford (so the attack is attempted and fails) and because all of this is very expensive the aim is often a sort of minimum acceptable margin of security against an ‘expected threat‘ (which might, mind you, still be a lot of security, especially if the ‘expected threat’ is very high). This is true of the castle itself, if for no other reason than that resources are scarce and there are always other concerns competing for them, but also for every component of its defenses: individual towers, gates and walls are not designed to be impenetrable, merely difficult enough.
This is particularly true in castle design because the individuals building these castles often faced fairly sharp limitations in the resources at their disposal. Castles as a style of fortification emerge in a context of political fragmentation, in particular the collapse of the Carolingian Empire, which left even the notional large kingdoms (like the kingdom of France) internally fragmented. Castles were largely being built not by kings but by counts and dukes who held substantial landholdings but nothing like the resources of Charlemagne or Louis the Pious, much less the Romans or Assyrians. Moreover, the long economic and demographic upswing of the Middle Ages was only just beginning to gain momentum; the great cities of the Roman world had shrunk away and the total level of economic production declined, so the sum resources available to these rulers were lower. Finally, the loss of the late Roman bureaucracy (replaced by these fragmented realms running on an economic system best termed ‘manorialism’) meant that the political authorities (the nobility) often couldn’t even get a hold of a very large portion of the available economic production they did have.5 Consequently, castle construction is all about producing what security you can with as little labor, money and resources as possible (this is always true of any fortification, mind you, merely that in this period the resource constraints are much tighter).
Knight Takes Rook
Of course in this context the expected threat is going to shape the calculation of what margin of security is acceptable, which brings us back to our besieger’s playbook. You may recall when we looked at the Assyrian siege toolkit, that many of the most effective techniques assumed a large, well-coordinated army which could dispose of a lot of labor (from the soldiers) on many different projects at once while also having enough troops ready to fight to keep the enemy bottled up and enough logistic support to keep the army in the field for however long all of that took. In short, this is a playbook that strong, well-organized states (with strong, well-organized armies) are going to excel at. But, as we’ve just noted, the castle emerges in the context of fragmentation which produces a lot of little polities (it would be premature to call them states) with generally quite limited administrative and military capacity; the ‘big army’ siege playbook which demands a lot of coordination, labor and expertise is, for the most part, out of reach.
Clifford Rogers has already laid out a pretty lay-person accessible account of the medieval siege playbook (in Soldiers’ Lives Through History: The Middle Ages (2007), 111-143; the book is pricey, so consider your local library), so I won’t re-invent the wheel here but merely note some general features. Rogers distinguishes between hasty assaults using mostly ladders launched as soon as possible as a gamble with a small number of troops to try to avoid a long siege, and deliberate assaults made after considerable preparation, often using towers, sapping, moveable shelters designed to resist arrow fire and possibly even catapults. We’ve already discussed hasty assaults here, so let’s focus on deliberate assaults.
While sapping (tunneling under and collapsing fortifications) remained in use, apart from filling in ditches, the mole-and-ramp style assaults of the ancient world are far less common, precisely because most armies (due to the aforementioned fragmentation combined with the increasing importance in warfare of a fairly small mounted elite) lacked both the organizational capacity and the raw numbers to do them. The nature of these armies as retinues of retinues also made coordination between army elements difficult. The Siege of Antioch (1097-8) by the First Crusade is instructive; though the siege lasted nine months, the crusaders struggled to even effectively blockade the city until a shipment of siege materials (lumber, mostly) arrived in March of 1098 (five months after the beginning of the siege). Meanwhile, coordinating so that part of the army guarded the exits of the city (to prevent raids by the garrison) while the other part of the army foraged supplies had proved mostly too difficult, leading to bitter supply shortages among the crusaders. Even with materials delivered to them, the crusaders used them to build a pair of fortified towers blocking exits from the city, rather than the sort of elaborate sapping and ramps; the city was taken not by assault but by treachery – a very common outcome to a siege! – when Bohemond of Taranto bribed a guard within the city to let the crusaders sneak a small force in. All of this despite the fact that the crusader army was uncommonly large by medieval European standards, numbering perhaps 45,000.
Crucially, in both hasty and deliberate assaults, the emphasis for the small army toolkit tends to be on escalade (going over the walls) using ladders or moveable wooden towers, rather than the complex systems of earthworks favored by the ‘big army’ siege system or breaching – a task which medieval (or ancient!) artillery was generally not capable of. The latter, of course, is a much more certain method of assault – give a Roman army a few months and almost any fortress could be taken with near certainty – but it was a much more demanding method in terms of the required labor and coordination. Thwarting escalade is mostly a question of the height of defenses (because a taller wall requires a taller ladder, tower or ramp) and good fields of fire for the defenders (particularly the ability to fire at attackers directly up against the wall, since that’s where the ladders are likely to be).
The other major threat to castle walls (apart from the ever-present threat of sapping) was catapults, but I want to deal with those next time for reasons that I suspect will make sense then. For now it is worth simply noting that catapults, even the mighty trebuchets of the 14th century were generally used to degrade defenses (smashing towers, destroying crenellation, damaging gatehouses) rather than to produce breaches. They could in some cases do that, but only with tremendous effort and a lot of time (and sometimes not even then). Consequently, for most castles the greatest threat remained escalade, followed by treachery or starvation, followed by sapping, followed by artillery.
A King In His Castle
The earliest castle designs we see in Europe during the Middle Ages are wooden ‘motte and bailey’ castles which emerge first during the 10th century and make their way to Britain after 1066. In the initial basic form, the core structure (the ‘keep,’ which is typically the fortified house itself) is placed on a motte, a hill (usually artificial) with a flattened top. The keep itself is constructed as a tall, wooden tower, with the height offering advantages both as a fighting position and for observation of the surrounding area. The motte is then enclosed by a wooden palisade (often two, one at the base of the motte and another at the crest) and surrounded by a ditch (the moat, which would be filled with water if it could be connected to a river or stream, but could also be left ‘dry’ and still serve its purpose), the dirt of which was used to build up the motte in the first place.
But as noted, the personal manor home of a significant noble (the rank in this case is often a ‘castellan,’6 literally the keeper of a castle, so entrusted by one of the more powerful nobles who holds sway over a larger territory; the castellan has the job of holding the castle and administering the countryside around it) is also an administrative center, managing the extraction of agricultural surplus from the countryside and also a military base, housing the physical infrastructure for that noble’s retinue, which again is the fundamental building block of larger armies. Which means that it is going to need more structures to house those functions: stables for horses, storehouses for food, possibly food processing facilities (bakeries, mills) and living space both for retainers (be they administrators or military retainers) and for the small army of servants such a household expects. Those structures (to the degree they can’t exist in the keep) are put in the bailey, a wider enclosed part of the settlement constructed at the base of the motte. As with the motte, the bailey is typically enclosed only by a wooden palisade; naturally that means the most valuable things (the physical treasury, the lord’s family) go in the keep on the motte, while the more space-demanding but less valuable things go in the bailey. There is a lot of room for variation in this basic type, but for now the simple version will serve.
The resulting fortification seems almost paradoxically vulnerable. The bailey, after all, is protected only by a ditch and a wooden palisade which a determined work-party could breach with just iron axes and an afternoon to kill. The core defensive motte with its keep adds perhaps only one more palisade and a steep climb. But in fact, these relatively modest defenses have greatly increased the cost of attacking this settlement. The motte and bailey castle, at least in its early wooden form, won’t stand up to a determined assault by a large and well-coordinated enemy, but that isn’t its purpose. Instead, the purpose of the motte and bailey castle is to raise the cost of an assault such that a potential opponent must bring a significant force and make a careful, well-planned assault; this the motte and bailey accomplishes quite well, which explains the long durability of the basic design, with stone versions of the motte and bailey persisting into the 15th century.
The quick mounted raid is now impossible; precisely because it will take a solid afternoon to breach the defenses, there is little hope of surprising the defenders. At the same time, the ditches will make any such work party vulnerable to missile fire (arrows, yes, but also javelins or just large rocks) from the palisade. And most of all, taking the place now demands you coordinate a work party, with some of your attackers splitting up to suppress the defenders, some making sure to block the exits so the defenders don’t rush out and attack your work party directly, and still more of your attackers in the work party itself. These very basic defenses have suddenly taken you from a position where a bit of surprise and rough numerical parity was enough to contemplate an assault to a position where you need several times as many attackers (for each of those divisions needs to be large enough to confidently win against the defenders if assailed).
Perhaps most importantly, the basic structure of this defense demands that you do this multiple times in sequence. We’ve already discussed the value of defense-in-depth, but in brief, every attack is at its strongest in the moment after it jumps off: everyone is alive, in the right positions, at the right time, coordinated and at least in theory clear on their objectives. Every movement and action beyond this point diminishes the power of the effort as coordination breaks down, attackers are killed and things break; this is what Clausewitz terms (drink!) friction – the unpredictable interaction of probabilities takes their toll on any plan, no matter how carefully designed. This is, by the by, more true in real warfare, where coordination is limited by communications technology, than it is in film or video games, where armies appear to mostly communicate by some form of instantaneous telepathy (it is amazing just how many clever sounding movie or game assault plans fall apart once you imagine trying to coordinate them with nothing more than shouting, or even a radio). As more and more things turn out unexpectedly or have to be improvised, the plan slowly shakes apart until eventually all of the momentum is lost.
The basic structure of a motte and bailey castle exploits this feature of warfare, forcing an attacker to overcome a series of obstacles in sequence, all while in contact with the enemy. Recall that this is a defense which really doesn’t envisage enemy artillery (because armies with lots of effective siege artillery were not common in the often small-scale warfare of the period; that’s not to say they didn’t exist, but if your motte and bailey castle forces the enemy to only attack with a big, expensive army that can build catapults, it has done its job, not the least because most possible enemies won’t have that capability at all), so an attacker is going to have to breach each layer in sequence while in contact with the defense and to pierce them all more or less ‘in one go.’ Consequently, taking the castle by storm means crossing (and probably filling in) at least one deep ditch, breaching a palisade under fire, then moving up a steep hill under fire, then breaching another palisade, at the end of all of which, the attacker must arrive at the keep with enough force and cohesion to take it. All of that is going to take a substantial attack and a lot of coordination and most potential attackers, the defender may hope, will lack either the resources or the determination to go through so much effort, especially as they are likely to have to do it multiple times: being entirely wooden, motte and bailey castles were fairly cheap and so a large territory could have quite a lot of them (note above on the Bayeux Tapestry how William has to take several such castles in order to capture Conan II of Britanny). Each motte and bailey castle thus raises the cost of trying to seize control of the territory; collectively they make that cost prohibitive.
Of course our principle of ‘antagonistic co-evolution’ is not done and the vulnerabilities of a wooden motte and bailey castle are fairly clear and easy to exploit. For one, the wooden palisade is mostly a blocking element, rather than a fighting position; attackers that reach the wall can actually use it as cover while tearing it down or setting it on fire. The entire setup, being made of wood, is vulnerable to fire but also to any kind of even-quite-modest catapult. And quite naturally, any military leader (which is to say, the military aristocracy which was emerging at the very same time as these castles) is going to want to build the kind of capabilities which will allow for successful castle assaults because, as we’ve already noted, castles function more or less as the ‘nails’ on the map which hold down the canvas of revenue extraction and military power.
Which in turn means evolving castle design to resist the methods by which a motte and bailey castle might fall. The most immediate change is in building material: wooden walls can only be so high, so thick and so resistant to fire. Stone, though far more expensive, offers advantages on all three fronts. And so, already in the late 10th century, we start to see stone keeps and gatehouses (supporting still wooden palisades); full stone castles would soon follow.
As an aside, one solution to this problem which doesn’t much appear in the Middle Ages but was very well-used in Iron Age Europe was what the Romans called the murus Gallicus, a hybrid wood-and-stone wall system. Gallic hillforts (called oppida) were built on hills, as the name suggests; their outer walls could be built by using earth fill to construct what was essentially a retaining wall, faced in stone, with transverse reinforcing wood beams every few feet. That created, in turn, a vertical stone surface, supported by the hillside itself, on which could be additionally built a wooden palisade for added height. The result was a very formidable fortification, assuming one had the hill to work with initially. You couldn’t knock it over or really undermine it effectively and the stone face was nearly vertical; the height of the hill meant that effective escalade meant coming up with a mole, tower or ladder taller than the hill (a thing, naturally, that the Romans ended up doing). That this style of fortification didn’t really reemerge in the Middle Ages speaks to the degree of path dependence in fortification design. Because fortification design tends to be evolutionary, it is possible in similar conditions to get very different responses as different designers try to meet the same threats by modifying different preexisting systems of fortification. That said, we’ll see next time something rather a lot like the murus Gallicus emerge to deal with the problem of gunpowder; the construction of Japanese castles (shiro/jo) also share many of the same principles.
As we move to stone construction and especially full stone construction (which we’ll define as the point when at least one complete curtain wall – don’t worry, we’ll define that in a second – is in stone) in the 12th century, we’re beginning to contemplate a different kind of defense. The wooden motte and bailey, as we’ve seen, mostly served to resist both raids and ‘hasty’ assaults, thus forcing less coordinated or numerous attackers to set in to starve the castle out or go home. But stone walls are a much larger investment in time and resources; they also require a fair bit more careful design in order to be structurally sound. For all of that expense, the builder wants quite a bit of a security, and in the design of stone castles it is hard not to noticing increasing attention towards resisting a deliberate assault; stone castles of the 12th century and beyond are increasingly being designed to stand up to the best that the ‘small army’ playbook can throw at them. Of course it is no accident that this is coming at the same time that medieval European population and wealth is beginning to increase more rapidly, leaving political authorities (read: the high nobility) with both the resources for impressive new castles (although generally the number of castles falls during this period – fewer, stronger castles) and at the same time with more resources to invest in the expertise of siegecraft (meaning that an attacker is more likely to have fancy tools like towers, catapults and better coordination to use them).
To talk about how these designs work, we need to clear some terminology. The (typically thin) wall that runs the circuit of the castle and encloses the bailey is called a ‘curtain wall.‘ In stone castles, there may be multiple curtain walls, arranged concentrically (a design that seems to emerge in the Near East and makes its way to Europe in the 13th century via the crusades); the outermost complete circuit (the primary wall, as it were) is called the enceinte. Increasingly, the keep in stone castles is moved into the bailey (that is, it sits at the center of the castle rather than off to one side), although of course stone versions of motte and bailey designs exist. In some castle design systems, with stone the keep itself drops away, since the stone walls and towers often provided themselves enough space to house the necessary peacetime functions; in Germany there often was no keep (that is, no core structure that contained the core of the fortified house), but there often was a bergfriede, a smaller but still tall ‘fighting tower’ to serve the tactical role of the keep (an elevated, core position of last-resort in a defense-in-depth arrangement) without the peacetime role.
While the wooden palisade curtain walls of earlier motte and bailey castles often lacked many defensive features (though sometimes you’d have towers and gatehouses to provide fighting positions around the gates), stone castles tend to have lots of projecting towers which stick out from the curtain wall. The value of projecting towers is that soldiers up on those towers have clear lines of fire7 running down the walls, allowing them to target enemies at the base of the curtain wall (the term for this sort of fire is ‘enfilade’ fire – when you are being hit in the side). Clearly what is being envisaged here is the ability to engage enemies doing things like undermining the base of walls or setting up ladders or other scaling devices.
The curtain walls themselves also become fighting positions. Whether on a tower or on the wall itself, the term for the fighting position at the top is a ‘battlement.’ Battlements often have a jagged ‘tooth’ pattern of gaps to provide firing positions; the term for the overall system is crenellation; the areas which have stone are merlons, while the gaps to fire through are crenals. The walkway behind both atop the wall is the chemin de ronde, allure or ‘wall-walk.’ One problem with using the walls themselves as fighting positions is that it is very hard to engage enemies directly beneath the wall or along it without leaning out beyond the protection of the wall and exposing yourself to enemy fire. The older solution to this were wooden, shed-like projections from the wall called ‘hoarding;’ these were temporary, built when a siege was expected. During the crusades, European armies encountered Near Eastern fortification design which instead used stone overhangs (with the merlons on the outside) with gaps through which one might fire (or just drop things) directly down at the base of the wall; these are called machicolations and were swiftly adopted to replace hoardings, since machicolations were safer from both literal fire (wood burns, stone does not) and catapult fire, and also permanent. All of this work on the walls and the towers is designed to allow a small number of defenders to exchange fire effectively with a large number of attackers, and in so doing to keep those attackers from being able to ‘set up shop’ beneath the walls.
Because it will matter next time, it is worth noting something about the amount of fire being developed by these projecting towers: the goal is to prevent the enemy operating safely at the wall’s base, not to prohibit approaches to the wall. These defenses simply aren’t designed to support that much fire, which makes sense: castle garrisons were generally quite small, often dozens or a few hundred men. While Hollywood loves sieges where all of the walls of the castle are lined with soldiers multiple ranks deep, more often the problem for the defender was having enough soldiers just to watch the whole perimeter around the clock (recall the above example at Antioch: Bohemond only needs one traitor to access Antioch because one of its defensive towers was regularly defended by only one guy at night). It is actually not hard to see that merely by looking at the battlements: notice in the images here so far often how spaced out the merlons of the crenellation are. The idea here isn’t maximizing fire for a given length of wall but protecting a relatively small number of combatants on the wall. As we’ll see, that is a significant design choice: castle design assumes the enemy will reach the walls and aims to prevent escalade once they are there; later in this series we’ll see defenses designed to prohibit effective approach itself.
As with the simpler motte and bailey, stone castles often employ a system of defense in depth to raise the cost of an attack. At minimum, generally, that system consists of a moat (either wet or dry), the main curtain walls (with their towers and gatehouses) and then a central keep. Larger castles, especially in the 13th century and beyond, adopting cues from castle design in the Levant (via the crusades) employed multiple concentric rings of walls. Generally these were set up so that the central ring was taller, either by dint of terrain (as with a castle set on a hill) or by building taller walls, than the outer ring. The idea here seems not to be stacking fire on approaching enemies, but ensuring that the inner ring could dominate the outer ring if the latter fell to attackers; defenders could fire down on attackers who would lack cover (since the merlons of the outer ring would face the other way). As an aside, the concern to be firing down is less about the energy imparted by a falling arrow (though this is more meaningful with javelins or thrown rocks) and more about a firing position that denies enemies cover by shooting down at them (think about attackers, for instance, crossing a dry moat – if your wall is the right height and the edges of the moat are carefully angled, you can set up a situation where the ditch never actually offers the attackers any usable cover, but you need to be high up to do it!).
Speaking of the moat, this is a common defensive element (essentially just a big ditch!) which often gets left out of pop culture depictions of castles and siege warfare, but it accomplishes so many things at such a low cost premium. Even assuming the moat is ‘dry!’ For attackers on foot (say, with ladders) looking to approach the wall, the moat is an obstacle that slows them down without potentially providing any additional cover (it is also likely to disorder an attack). For sappers (attackers looking to tunnel under the walls and then collapse the tunnel to generate a breach), the depth of the ditch forces them to dig deeper, which in turn raises the demands in both labor and engineering to dig their tunnel. For any attack with siege engines (towers, rams, or covered protective housings made so that the wall can be approached safely), the moat is an obstruction that has to be filled in before those engines can move forward – a task which in turn broadcasts the intended route well in advance, giving the defenders a lot of time to prepare.
Well-built stone castles of this sort were stunningly resistant to assault, even with relatively small garrisons (dozens or a few hundred, not thousands). That said, building them was very expensive; maintaining them wasn’t cheap either. For both castles and fortified cities, one ubiquitous element in warfare of the period (and in the ancient period too, by the by) was the rush when war was in the offing to repair castle and town walls, dig out the moat and to clear buildings that during peace had been built int he firing lines of the castle or city walls.
Speaking of which…
The main difference in defending a town rather than a single fortified private residence is the area that needs to be defended: the town core is naturally much larger than the size of a single keep or bailey and so the circuit of walls surrounding it also needs to be much longer. That longer circuit, of course, means a higher cost in terms of constructing and maintaining the defense, but the advantage a town often has here is its own residents: the populace of a town often has a fair bit more labor to devote to defense construction compared to the medieval aristocracy who mostly draw their power and resources from the more thinly populated rural countryside.
Nevertheless, the larger size of the area being defended makes it harder to deploy concentric defense-in-depth solutions. There are also transit considerations: towns are, after all, economic centers, typically sitting at the junction points of many different local and regional routes, which means they tend to need lots of entry-points to facilitate all of that travel and trade and in turn that means lots of potentially vulnerable gatehouses. Meanwhile, internally, the desire for residents to move around the town freely and general land-use considerations make subdividing towns into walled districts (very common in video-games for memory-management and loading reasons) very difficult and as a result very rare. You can see this, for instance, looking back at the period city-maps from the Lonely Cities series: a good number of cities have either a citadel or a section of the town which is walled but also outside of the main circuit (often separated by a river), but full concentric styles of defense or multiple cell-like walled districts don’t really occur. There are exceptions, but they are relatively rare: most cities have a single primary circuit of walls, which, if they are breached generally give access to the main area of the town.
In Europe, the most complete and formidable set of city walls were without question the Theodosian Walls built to defend Constantinople during the reign of Theodosius II (r. 402-450). The Theodosian Walls stood for the whole Middle Ages but they really reflect the culmination of the ancient system of city wall fortifications, the ultimate answer to the kind of ‘big army’ playbook the Assyrians (and Romans) employed. So I want to both talk about the defense system but also note points where its method diverges from the walls of later medieval towns.
The Theodosian Walls had to cover some 5.7km and had nine gates; both numbers should immediately make clear that you needed quite a few people to man these defenses effectively. This was in particular a factor for town defense: most of the defenders are going to be citizens of the town called up to defend it in an emergency, rather than a standing guard. As far as I can tell, this seems to have made towns somewhat more vulnerable to surprise ‘hasty assaults,’ if the attacker could force a gate along a long circuit before the defenders knew where the attack was coming. Of course that problem is intensified by the fact that this is a single-point-of-failure system: the loss of one gate against a superior foe generally meant the loss of the town.
The Theodosian Walls are unusual in that they are a set of triple walls. The main fighting position was on the inner wall; in front of this was the peribolos, a low, flat, unobstructed gap, after which was the lower outer wall, a secondary forward fighting platform. The towers of the inner wall project out into the peribolos for exactly the same reason castle towers project: defenders on those towers can fire, unobstructed, down the peribolos, meaning that an attacker can find no safety here. The crenellation of the outer wall likewise only faced out, so attackers who seized the outer wall would have no cover from defenders fighting from the inner wall. Next, after another gap was a simple low forward wall, little more than a stone breastwork about 1.5m high. Finally, the low wall stood at the inner edge of a large moat, some 20m wide and 10m deep, because no good defensive system is complete without a ditch.
That low wall is a kind of what we call an ‘outwork’ (we’ll see a lot more examples next time of forms of outworks). This particular kind of outwork is a product of the ancient world and uncommon in medieval fortifications to my knowledge; it was a response to the increasing use of torsion catapults during the Hellenistic period. While it did offer a position for defenders to use to sally out (for instance to destroy enemy siege engines), the primary purpose was to prevent enemy catapults from being able to direct fire at the base of the main wall and its towers. Even if knocked down, such an outwall’s rubble would obstruct direct fire on the curtain wall or the towers. This idea – using an outwork to physically block lines of fire on the curtain wall – is going to come back a bit later.
In contrast, most later medieval town wall circuits generally only have a single curtain wall, supported by a moat. As with castles, the wall is supported by projecting towers which can direct fire along its length and hardened gatehouses. Where cities sometimes do employ defense-in-depth it is with a ‘citadel’ – a hardened fallback position either inside the city or (more often) built in to the wall circuit; essentially a complete castle built into the city wall. The role of the citadel is important for thinking about what these defenses are intended to achieve: defenders who have lost the main area of the city but have held out in the citadel are unlikely to be in a position to recapture the city or even to seriously threaten to do so. But the citadel has important negotiating power. Even a small number of surviving defenders can likely hold a citadel (with its stockpile of supplies) for a long time; taking such a citadel by storm poses all of the problems of storming a castle, with the added disadvantage of having to do so through city streets. Consequently, defenders holed up in the citadel are in a good position to negotiate for terms: perhaps being able to march out unharmed in exchange for turning over the citadel, or else negotiation less onerous terms for the city in general (alternately, they might try to hold out until a friendly relief army could arrive).
And that brings the focus to something important about almost all medieval siegecraft: the siege and negotiations generally proceeded side-by-side. By raising the cost of a siege (either a blockade or a storming assault), the defender could improve their bargaining position, even if they were always going to have to surrender. Meanwhile the attacker, by very visibly preparing for a deliberate assault could signal to the defenders their resole and thus attempt to encourage surrender. As far as I can tell, far more fortified medieval towns and castles surrendered than were ever taken by storm and so consequently a lot of this fortification work is as much about shifting bargaining positions in the event of an attack as it is resisting an attack.
Next time, we’re going to move a bit forward and look at the impacts of artillery, both catapults and more importantly gunpowder on this system and in particular at a new system of European fortifications which emerges to deal with gunpowder armies.
- I struggled for a good term for ‘defenses designed to protect a single settlement and settled on ‘point defense’ in its most general possible meaning as encompassing the point reasonably well. Of course point defense can mean something rather different in a modern, technical concept, although the definitions are linked.
- That said, strategies of raiding and devastation were common in the Middle Ages in the small-scale warfare between nobles and sometimes even in the larger scale warfare between kingdoms. If your goal is merely to weaken your enemy, you don’t need to take the castle – you can inflict enough damage on the countryside by raiding to deny your opponent income and thus degrade his ability to raise and supply his own armies. The high difficulty of taking castles is what makes this sort of strategy so attractive.
- The Romans are also really good at taking fortified settlements, to the point that effectively no fortification could be expected to stand against a determined Roman army. That really changes the calculus, but most medieval armies simply lacked the resources, size and coordination to match Roman siege engineering.
- By which we should understand ‘center for the extraction of the countryside’s agricultural surplus and then the spending of that surplus’ because that is essentially what ‘administration’ means in the pre-modern world
- Something that could, by the by, be good for your average farmer. In the pre-modern world, where there were strong limits to how far economic productivity could be increased, highly effective taxation systems might push the actual everyday farmers closer and closer to subsistence. The degree to which the loss of economic complexity through trade and urbanism could be balanced by reductions in effective taxation is something it looks like we’ll be discussing fairly soon, given the current balance of votes in the ACOUP Senate
- Or one of many such equivalents or near-equivalents. While games tends to present medieval titles as a single, coherent logical system, in practice there is a bewildering array of titles whose definitions shift from one area to the other and aren’t always even equivalent across systems.
- Just to be clear, the ‘fire’ we are discussing here is still muscle-powered, not chemically powered (that is, arrows and javelins, not muskets). Nevertheless, in military terminology, any weapon-system engaging at range is ‘fire’ (as compared to ‘shock’) and we’re going to stick with that terminology even when we are dealing with arms that do fire that aren’t firearms. Alas that modern military terminology was not designed for a pre-gunpowder context!