Fantastic Fortress: Attacks from Below

Continuing the discussion I started here and here lets discuss the possible dangers from below a fortress in a typical fantasy setting might face. As outlined in the previous post the two major threats from below are 1) enemies digging tunnels to mine the walls or enter the city covertly, and 2) more natural threats which might threaten the foundation of the entire region such as nonintelligent tunneling worms(purple worms and their relatives) creatures that can cause earthquakes or other effects such as spells that turn rock to mud or move earth, etc.

1. Mining

For the first problem we can stick to historical solutions, as historical siege warfare regularly involved tunneling in both attack and defense. Essentially this involves counter-mining by the defenders, this can be done in one of two ways, digging a tunnel to intersect with the attackers tunnel and trying to overcome their miners in a "battle for the tunnels" with the goal of preventing them from finishing their mine, or digging a tunnel underneath the attackers tunnel, ie "undermining" them, and then collapsing the the tunnel below in the hopes that the attackers tunnel will collapse in turn.

These solutions sound simple enough but their are a number of factors that make them difficult. the first of which is detecting where exactly the enemy tunnel is. This is an even bigger problem in a fantasy world when there are entire groups of people who live underground and may already be beneath the fortress. 

In standard siege warfare it is almost always possible to recognize when mining is taking place due to the excavated earth that must be dug out. Mining costs a great deal in manpower and so is usually begun relatively close to the fortress walls allowing the defenders to realize that mining has begun even if the exact location of the mine below is not obvious. Luckily the sounds of mining can be quite loud underground and can sometimes be detected by sentries posted in cellars near the castle walls. Detecting the vibrations of enemy shafts can also be accomplished by setting out a bowl of water and observing the vibrations tin the bowl. Of course detection of mining can be made much easier by the use of magic in a fantasy setting.

Other options for detecting enemy mines involve digging test shafts under the wall in the hopes of intersecting the enemy mines, but this can often be a noisy affair underground warning the enemy that their mine is in danger and is not guaranteed to succeed. Another defense would be to dig defensive mines intended to intersect any probably places where an enemy might try to mine the walls. with these prepared mines, warriors can already be placed for defense. however this defense assumes the attackers wont undermine the defenders mines, and also that the defenders can hold the mines. if the defenders fail in the mines, that leaves a way open for the attackers to bypass the walls of the fortress altogether.

If the enemy is in the early stages of mining, the defenders might attempt to increase the width or depth of their moat, provided the fortress has one. Other defensive options once a mine is found involve introducing dangers to the miners themselves: such as flooding the mine, introducing bees into the mine, or other wild animals such as bears or wolves or attack dogs, this could include more dangerous monsters in a fantasy setting. The defenders could also release smoke or other poisons into the air to kill or drive away the attackers.

Another possible defense against mining is simply to simply construct the fortress on ground that it is impractical to tunnel in. This can vary from extremely hard stone to building over an area of sandy ground or wetland where the soil will not support a tunnel. Building near a wetland or body of water may prevent mining as the intended mine may be flooded by the high water table below ground. This isn't a guaranteed defense though as there are methods of draining or pumping the water out of these mines.

In conjunction with the above, the best defense against mining is really the construction of the fortress itself. By building the fortress with circular designs, ie round towers instead of square, the walls become harder to collapse; often the corners of fortress walls are the most vulnerable to collapse from mining. another method of defense via construction is to increase the sheer size of the walls. The larger or wider the walls are the less threat there is of a collapse. This is what happened historically with fortresses as cannons made stone walls obsolete; fortresses were built with large earthen ramparts that would not collapse in the same way as thinner stone walls.

In the case of miners from below such as goblins or dark elves many of the above defenses can be employed with modification. These attacker presumably would not have the goal of collapsing the walls of the fortress but tunneling directly inside it. Of course other methods to stop mining from below include building near water or on extremely hard rock, etc. the same would deter mining in a siege scenario. IN cases where this is not possible, defenses such as countermining, and detection of enemy mines would apply here as well. This is the case where a pre-dug series of mine galleries beneath the fortress may prove most beneficial. If tunnels are made by the defenders to stop enemies from tunneling from directly below so that they must encounter the mine galleries of the fortress first, that can slow them down or even stop them from reaching the fortress. These galleries can be constructed with chokepoints and appropriate defenses, such as caged beasts or monsters ready to be released when needed, sections of tunnel designed to be collapsed, etc. Creating these galleries in a mazelike fashion so that a someone unfamiliar with them would get lost, with secret passages for a more direct route of retreat could prove to be a common defense. Essentially we have invented the classic fantasy dungeon again but as a method of protection. 

2. Foundations

The second threat, that to the foundation of the fortress more generally is a bit harder to solve. some of it has been touched on above, building the walls to be wider so that they don't collapse as easily, but this only addresses the wall of the fortress and not the entre structure. Looking at methods of defending against earthquakes seems to be the most logical avenue of approach to this problem. 

The building materials of a fortress need to have some degree of flex to withstand the lateral forces of an earthquake or shifting ground. Unreinforced masonry(brick) and stone is the least stable and can crack or totally collapse when shear forces are applied; while wood(if properly anchored) and reinforced concrete allow the building to to flex when the ground beneath shifts. 

Another way to withstand the forces applied to a building during a quake is to isolate the base of the structure from the foundation. In modern buildings this done through the use of concrete columns reinforced with steel, or other methods such as the use of rubber pads. In a fantasy setting we can assume that steel reinforced concrete is out of the question, as is rubber. Instead we might assume magic could be used to accomplish the same goal; levitating the entire structure a few inches or feet off the ground. This could also be a method of deterring mining attacks. However, in this series I am looking to propose solutions that don't resort to the fantastical and could be made to work by a less technologically advanced society. As a result I don't see base isolation as a feasible solution.

Other factors can contribute to the stability of a structure. Avoiding load bearing columns on the ground floor, as well as decreasing the number of windows and doors that might weaken load bearing walls on the ground floor can make a structure more stable. Also using shear walls, ie walls that extend from the foundation to the roof, can reinforce the integrity of a structure; this precludes the stereotypical quasi-medieval building with haphazard floors in a jumble of patterns and designs that have been added over the years. Also the use of triangles in building design may prove to be more prevalent in a fantasy setting for the same reasons and triangles(and pyramidal) can withstand greater forces than other shapes under pressure. Another thing that might be counterintuitive is that taller building are more flexible than shorter ones; this is because tall buildings, if constructed of the right materials, can sway back and forth to relieve the forces applied at the base.

Another thing to keep in mind is that harder bedrock is more stable than softer or sandy soil. This may seem common sense, but with creatures that eat through rock, people may look to build on bedrock that is less prone to collapse. When the soil does collapse and the foundation of a building shifts, it might be prudent to have drains already built in to the structure in order to drain off any excess water or sewage from below ground wells, sewer systems, or septic tanks.

Fantastic Fortress: Dangers of the World

Before considering how a fortress may optimize its defense in a fantasy kingdom, it's necessary to first look at all the possible threats present in the fantasy setting. I'm dividing threats based on Air, Overland, and Underground origins. I posted a thread on Dragonsfoot and ENworld for ideas on what other possible threats might be present in a fantasy setting.

We already looked at airborne threats in the last post. It occurred to me that the auditory detection system might not be effective against most fantasy flyers. I doubt even dragons make the kind of noise small prop aircraft do, so maybe a detection system based on sight alone might be better. I'll have to think on that one. One thing I didn't consider was breath weapon or area effect attacks, particularly form dragons. These could include fire, gas, poison, etc. So the aerial defense would have to also take into account a way to mitigate damage from breath attacks and not just the flyers themselves.

There are only a few possible underground threats and they all have a similar effect. These threats would include Humanoid diggers, whether they are other human armies,goblins, orcs, etc; they could all be countered according to traditional methods from historical warfare. Other Underground threats would involve unintelligent burrowers such as purple worms, and creatures or magic that cause earthquakes or otherwise threaten the integrity of the foundation of a fortress such as stone to mud spells. All these underground threats have a similar effect, the undermining of the foundation of castle walls or the bypass of them by digging under. The best defense would not be a strategy made for each individual threat, but some way of shoring up the foundation so such threats will rarely be effective.

There are number of land based threats. These include Giants and other Huge monsters which could destroy walls due their sheer size. Also creatures which can climb sheer walls such as aranea, footpad lizards and such make traditional castle walls obsolete. And finally there are the tiny creatures, such as brownies, that could slip past normal castle defenses with impunity.

There are a few other threats which I won't be taking an in depth look at because I think the best defense against them would be magical and not structural in nature. There are creatures a spells which may ignore the physical entirely by becoming ethereal or teleporting. There are creatures with gaze attacks, which might be feasibly defended against without magic, but I don't see such creatures as being so common as to threaten an entire fortress; they tend to be rare solitary creatures. Then there are creatures that have charm effects which negate whatever defenses you might have, the only reliable defense against a charm is another spell.

Fantastic Fortress: Attacks from the Air

I've been doing research lately on historical anti-aircraft tactics. Looking at what has been published in places like Dragon magazine and then suggestions on the internet about how best to defend against aerial attacks don't satisfy me. Typical suggestions rely too much on magic especially spells specific to D&D, or monsters being tamable. There has to be a more mundane, simpler and cost effective method to defend against aerial attacks from flying monsters, like dragons, with ancient/medieval levels of technology. This article is going to be the first in a series of posts about how a castle would change to defend from the fantastic attacks inherent in a standard fantasy world.

Historically there seems to be 4 main methods to withstanding an aerial assault: defensive aircraft, advanced warning systems, anti-aircraft guns, and bomb shelters. I am going to detail possible fantasy analogues for each method of defense that relies on mundane techniques and not magical spells.

Concerning flights of fighter planes to defend air space, the most common thing that seems to pop up on the internet when air defenses are talked about are flights of knights on trained hippogriffs. Even in a high magic setting I find this solution extremely implausible. I consider hippogriffs to be more like zebras in temperament than a horse. If we're going to go with flying mounts the most likely creature would be a Pegasus or pegataur, but that still requires a setting with all the prerequisites for raising and feeding and training these mounts. They would be obedient to their rider and probably no one else. We would see only the elite with these types of mounts. Whatever the mount is it would have to be domesticated, easily stabled and fed and with an easy way to ride them and still use weapons of some sort. An alternative to a mount would be to befriend a flying beast who can ward off hostile monsters. This could be a lawful dragon or sphinx, or even a flying construct of some sort made specifically for this purpose.

Creating equivalents of advance warning systems may prove to be the most daunting task I have set for myself. Barring magical scrying techniques(and who can afford to pay those extortionist wizard fees anyway) there is no low tech version of radar. Therefore, it is necessary to look to solutions that were used in war before the advent of radar but after the invention of flight. One example used towards the end of WWI was an acoustic detection system. Relatively primitive methods were used at first with multiple metal cones used to identify the distance and direction of incoming aircraft. This was later developed into huge concrete sound mirrors and walls.

German Acoustic Locator 1915

British Sound Mirror 1928

British Sound Wall 1930  

The sound mirrors could detect aircraft 20 to 30 miles away, and with the proper electronic equipment a range of up to 50 miles was claimed. Even without electrical amplification the utility of these devices was impressive. Of course in a low tech environment concrete would probably not be used. It might be more economical to make the large mirrors/walls out of stone blocks or carve them into a mountainside. In either case such an endeavor would require vast resources only available to a large organized state and not a standard feudal kingdom. In the case of less centralized governments the small mobile or personal sound locators might be more common. Regardless the most intelligent use of these devices would be to have several near the outer boundaries of the territory with a line of signals, whether that be fires or reflective mirrors or pigeons, to alert major areas of population about incoming threats.

















Concerning Anti-aircraft guns, this seems to be the easiest solution to solve. As a replacement for the guns themselves, ballistae could prove useful. The ballista could even be modified in a way to fire multiple missile in quick succession similar to the chinese chu-ko-nu.

Think this but big enough to kill a dragon

Other factors play into anti-aircraft than just the guns though. The use of mobile guns and emplaced guns working in conjunction was essential. Both of these are fairly simple to accomplish with ancient technology. Mobile guns can be placed on carts or boats or even simple rail systems(mule powered) connecting key areas of defense. During the latter part of WW2 the germans built several concrete fortresses to mount big anti-aircraft guns on. They were built in pairs, one had lighter defenses and was focused more on range finding while the central one caused the most actual damage to aircraft.

Looks kinda like a castle, huh?

Again these wouldn't be a grand change for medieval architects, simply adding emplacements for ballistae on top of a castle would probably suffice. Though in some cases height may be an issue, as the german towers were more than 100 ft tall and most historical castles didn't reach those heights as far as I know. Height/range may also prove an issue for ballistae too; the range of historical ballista was nothing like a standard flak gun. I guess it depends on how high the target is flying.

The last aspect of air defense seems to already be solved for us. Pretty much every castle and city in most fantasy worlds seems to have underground mazes and dungeons of one sort or another. A logical explanation for the purpose of such complexes is as bomb shelters. So, problem solved right? Probably not. I don't see a real need for bomb shelters in a fantasy world. Dungeons are still an inexplicable mystery for the most part. The problem is this; in a typical fantasy world there are no bombs! What is the point of a bomb shelter without bombs? Yeah, OK, an enemy could take a lot of big boulders and use flying mounts or spells to drop them from great heights(something pretty common in most games I have played), but these simply don't have the destructive power of actual exploding bombs. Without gunpowder or an equivalent to construct exploding shells the use of a bomb shelter is doubtful. Yes, being underground would protect against falling rocks, but so would a sturdy roof made of stone and angled in such a way at to deflect incoming missiles. This may prove as a point in favor of building underground to begin with. But this may cause other problems which we will get into next time.

The next post in this series will discuss threats from below for a Fantastic Fortress, and after that we may discuss the effects of D&D magic or land based monsters, and then finish with an example combining all elements and compare it to historical castle construction.