How to build a fortress to survive against mythical creatures

Question

I need a fortress that will stand up to the following magical creatures, must be above ground and have a fairly large (20-50 thousand) civilian population as well as a roughly equal number of soldiers, middle-ages level technology:

• Dragons: Enormous (75-100 ft. long) flying creature, arrow proof (although a quarrel at fairly close range will pierce them) scales everywhere but wings, breaths fire, low (cow-like) intelligence.

• Drakons: Much smaller, (10-12 ft. long) flying creatures, similar scales to dragon, cannot breathe fire, pack hunters (groups of 10-20) , medium (dolphin-like) intelligence.

• Orthrus: Two headed, 4 ft. tall wolf, thick steel fur that can deflect slashing attacks, pack hunters (20-30) , medium (dolphin-like) intelligence.

• Diatrima: Enormous carnivorous birds (8-10 ft. tall), axe-like beak, live in groups of 3-4, low (cow-like) intelligence

• Feralt: Humanoids with various animal features (eg. ram's horns, wolf fangs and muzzle, feathers, claws), live in tribes of 500-1000, but will band together in large, 10-15 tribe alliances to attack the city, use Diatrima and Drakons as mounts, use Orthrus as hunting/war dogs, high (slightly sub-human) intelligence.

• Spinterra: 20 ft. long porcupine with venom-coated steel spines that they can launch up to 75 ft. Can burrow (fairly quickly) through most substances including rock. Low-Medium (Lion-like) intelligence.

• Squirreloid: 5-6 ft. tall bipedal squirrel with extremely sharp teeth and claws. Very High (human) intelligence. Can climb most surfaces easily, but fairly rare. Do not work together with Feralts. Live in teams of 10-20.

The biggest goal of all these creatures is to kill as many humans as possible, low intelligence creatures merely attack all humans they see, Feralt make complex military alliances and attack plans.

Humans (but not creatures) have access to magic with the following laws:

1. All magic requires runes and a verbal activation (saying 'magic words' that correspond to the runes)
2. Any spell lasts a maximum of one minute (no enchanting)
3. Any spell has a certain maximum amount of power, and will not complete tasks over that power (you can create a small fireball, but can't make a storm or teleport)
4. Any spell takes three seconds to take effect after the verbal component has been said (gives time for a counter-spell)
5. Runes can be traced on a surface (temporary rune) and can then be activated only by the maker, or engraved/written (permanent rune) where they can be triggered by anyone holding the object.
6. All enemy creatures carry a radius (roughly their own length/height on each side of them) where magic cannot affect anything (but you can do things like throw a rock with magic into the radius, it just stops being propelled by the magic, but keeps its momentum)

I would also like to know if you find any loopholes using this magic system allowing things like teleportation or mind-control, anything I probably wouldn't like.

Answer 1

Weaponize minor magic.

Make the walls of your fortress at a slight incline, and have storage areas for oil and/or tar. Let the oil flow down and ignite it with small fireballs to take care of the land-based attackers. Fire ignited by magic, but natural once started negates dispel effects.

For the aerial creatures, target a wing with ballistae firing metal bolts, use the rune magic to heat or chill the metal for extra damage. You could also charge the metal bolts with electricity (think capacitor) and let the electricity discharge when it hits its target.

Runes firing off sound blasts next to the aerial creatures could stun them and cause them to fall, making them vulnerable to ground attacks.

Another combination to affect all of them would be spraying oil into the air in a fine mist, using a wind spell to spread it over the enemy, and then a fire spell to ignite it.

Illusions to confuse the less intelligent creatures to make them think they were being attacked by their allies would work as well.

Answer 2

The answer is "you don't" - there are better ways to defend against all those mythical creatures once you introduce a magic system.

The beauty of having a magic system means you can counter all of your magical creatures by designing a single handheld weapon for your soldiers - and it's not even a siege weapon.

All you have to do is design a magical pellet launcher - it launches pellets at high velocity in quick succession, and changing up the pellets also allows you to create "flak" pellets for anti-swarm purposes.

How would this work? Simple: Have a bamboo shoot where runes are prescribed; the runes create a directed force out the end of the bamboo shoot. With some engineering, you could continuously load in pebbles which will be accelerated as a bullet. If you load in an "activated, explosive rune inscribed rock", you can make use of the 3-second delay in activation of the spell, and activate the spell just before you launch it so that it explodes into a spray of rock in the air after traveling for 3 seconds.

But how much energy is really required? How much force? Well, consider that a .44 magnum has a muzzle energy of 1400 joules. A "fireball spell" costs 1568 Kj (according to this question, which means you're able to output 1568000 joules in a single spell. That means you can regulate it to fire 1120 .44 magnum-sized pebbles in a single minute - congratulations, you've just discovered the medieval chain gun with 1120 rounds per minute capability and a 3 second recharge time.

Who needs to build walls differently when you can just mow down any swarm of enemies coming at you?

Of course, those are only the magical weapons for general daytime war, for passing it to your most standard soldiers.

You can create something better - you can create sniper rifles. High-velocity sniper rifles. Railguns. Let's aim for the top of the list, the heavy arty to take out the heaviest biggest flying menaces - although our chaingun should be enough to rip their wings to shreds and tear holes in the scales, we want to look awesome, so we'll build a railgun.

A railgun typically uses around 50 megajoules of energy - each rune you prescribe can hold 1.5 megajoules, so if you chain 34 rune inscribed tubes together, you can accelerate a nicely shaped rock to railgun level speeds. Goodbye dragons!

In short: everything on the ground but far away dies to railgun (even when the railgun misses), everything in the air dies to chaingun and railgun, and chaingun rips any advancing ground-based troops to shreds for fun.

Edit: For the new burrowing creature, a series of railgun shots propagating in a circle outwards from the walls aimed at the ground will kill pretty much anything underground. According to this impact calculator a 25 cm diameter rock fired at the ground at rail gun velocities of (on the lower end), 3 kilometers per second, at a 45-degree angle, there will be a crater with a 3-meter diameter, nearly 1-meter depth. Against a 20 meter long underground target? You can be pretty sure that you'll kill it or at least dismember a part of its body from forcing the dirt through its body via impact.

Answer 3

First, you need a roof unless you want your unexpected guests just dropping in for dinner.

Since your magic system seems to make some kind of "magical forcefield" unworkable, that roof has to be physical and able to keep out big things.

The best way to get a strong roof is to build underground or into the side of a cliff. Think of the dwarven kingdoms in Lord of the Rings or the Hobbit.

If that isn't possible because you need to build a town in the middle of a fertile delta for shipping and agriculture, make a lot of high walls and narrow walkways. It's not a perfect defense but if the dragon has to tear down walls just to get at the people walking between them, it helps.

Especially in the last case, the further away you can engage the creatures, the better. Magically powered ballista would be good (think coil gun for spears). Create a hopper above the ballista to carry a bunch of ammo. Cast your 1 minute long spell and start hosing down the enemy from a distance. A few of these on the walls will discourage large snackers.

On a smaller scale, crossbows with a similar setup would make good "machine gun nests" to take care of the humanoid opponents.

Answer 4

You build on water. I took a bay with a river delta and a surrounding area of swampland.

1. Castle, food stores, stone foundation.
2. Market area, stone foundation, walled and gated.
3. Church or otherwise significant location, stone foundation because people mass there
4. Harbor, way to get food in and out as roaming groups aren't known to posses ships. None of the animals seem to be that dangerous in the water.
5. Gated river entrance. Perhaps large metal doors with bars behind it that sink deep into the river/ground.
6. not yet visible
7. not yet visible
8. Swampland. Metal hided animals are to heavy, they will sink and drown. Dragons are also far to large to land here.
9. River gives access inland.
10. Tower with ballistas against flying enemies. Create overlapping arcs of fire against besiegers that storm the walls.

You build a wall around the edge of the water. A thick stone wall, maybe Roman concrete. Think like the Great Wall of China. It needs large towers that go outward to create overlapping arcs of fire.

Number 10 is such a spot. You also mount them with ballistas. Each round probably enchanted, with runes, to do maximum damage to flying enemies. Perhaps it never misses, perhaps it's on fire or perhaps it splits into multiple smaller projectiles. Maybe it does all three. It's magic. You fill your city with wooden housing on poles. The enemies can't breathe underwater. This way the burrowing enemies can only attack the walls. The walls are manned by your soldiers and guarded.

Wood is cheap and relatively light. Houses are expected to be lost but can be quickly rebuild. The local abundance of water helps with fires and it's easy to keep the wood wet to prevent them in the first place.

6. Villages near the road and river. Farms inland provide the food needed what the lake can't bring.
7. Wooden houses and roads.

Not last but least, you deploy large grates over your city leaning on stone foundations. They're just small enough enemies can't get through. They're lined with copper. Why? Because you deploy mages to set that under a current when the enemy lands on it. Shoot lighting on it or something like that.

Why does it work

Anything that climbs or burrows the walls will be confronted with water. They might swim but fighting and swimming at the same time is hard. The water gives you unlimited supplies, outlasting any siege.

Flying enemies could fly over the wall but the heavier ones can't land. They would simply fall through the wooden floors, into the water. The Diatrima are likely light enough as they're hollow boned birds I assume. But they lack scales and are therefor easily brought down with ranged weapons, especially while landing.

Feralts are primitive tribes that band together for campaigns. It seems unlikely they can coordinate a long siege. They lack the organization to keep themselves supplied. To lock down the city they need a navy. One bigger then our city, something that would require a city in comparative siege to support. If they had that they wouldn't be tribal I figure.

Dragons sitting down in your roofs seem the main problem. For the rest you build walls seven feet thick with openings small enough for one or two humans to pass but no big monsters.

Old answer before edits:

So about those roofs. One way could be extra high walls. Your roofs won't attach at the top but much lower. So the top of your fortress looks like a second floor with no roof. If you get the top of the walls thin enough they would make terrible spots for your dragons to sit on. Of course you need three or so feet down some extra support so your Drakons don't push them over.

I suggest rooms to be sunken in the ground for maybe the first story. Then one story up to the real roof. Speaking of the roof you likely want that to be fire proof. Same goes for the outer doors. Perhaps metal can be used. It would be heavy though so I assume only to be closed during attack.

Really though flying enemies the size of dragons that can be mounted are an awesome siege weapon. I guess those seven foot thick walls with small hallways between them and plenty of support might keep them out. If your defenders keep killing them fast enough.

Farms etc would obviously remain outside and burned to the ground.

Answer 5

The magic of your technology is similar to the medieval technology.

The attacking powers are much stronger - it is because they can fly.

In the lack of intelligence (even the feralts aren't comparable in intelligence to a mediaval attacking army of knights), I don't think that they could mean any danger for a mediaval-like castle fortress, whose defenders are using magic instead of medieval technology.

But the flying enemies are a major problem.

I think, also the dragons aren't very dangerous, because - although they can fly -, but they are stupid. Yes, they are arrow-proof, but they aren't fire-proof.

How would they defend themselfes against wizards teleporting burning tar into their eyes?

Well, you say they have an antimagic field around them. Ok, then wizard1 makes a cup of tar invisible, wizard2 teleports it to the border of their antimagic field, wizard3 shots it into their eyes, wizard4 make it firing, wizard5 explodes it. Wizard6 could manipulate the spells of the others with same meta-magic to get a proper time synchronization.

The diatrima would be expelled very fast and they would learn also very fast to leave any human stronghold far, far away.

I think, drakons are far, far the worst enemy.

Combining the flying with the dolphin-like intelligence and organized group-activity will result, that only very proper combat maneuvers could defend the stronghold against them.

"Normal" magical solutions won't work against them, they would learn what humans do and next time they will avoid it.

What to do against drakons? Their advantages, compared to humans:

• flying
• magic resistance
• carnivore monsters

The advantages of the humans:

• intelligence
• magic

So, the humans would need to use intelligent magical solutions against the drakons. They would need to continuously invent newer and newer combat tactics, what the drakons didn't learn until that point.

The ideal meta-strategy: humans will have with the drakons a rock-paper-scissor game. They have their tricks, the humans have their tricks.

Everything what humans can do, could be avoided by the drakons, and all drakon strategy will lose against the proper human strategy.

But, the drakons still have a limit: their "library of strategies" isn't infinite. But the humans', yes.

After a lot of fights, the humans will win on the long-term, simply because they can learn and use millions strategies and the dolphin-level drakons can only some hundreds-thousands.

Extension: I have a new idea.

You didn't mention their non-magical technology, but indirectly I suspect it is also on a medieval level. It results, that the humans have essentially two useful technologies:

1. Medieval non-magical technology (composite long bows, swords, burning tar)
2. And also a magical technology which is around so effective as our non-magical, medieval one.

Combine them.

I think on:

• magically targeted arrows
• magical "radars" (divination school) predicting the arrival of the enemy
• various manipulative illusion spells to undermine their strategy

I think it will handle also the drakons, until they aren't in overwhelming majority.

Answer 6

Here are some ideas how to strengthen the fortress to repel those magical creatures.

Spear guns: have a big tube with a large piece of rock that blocks up the whole tube, the rock is lifted, then spears are put in holes that attach to the big tube, when you drop the weight, away they go. This probably wouldn't have an amazing range but you could still shoot a good distance with them.

Mirror Spotlight: using an array of mirrors you could build a fairly good spotlight that might scare enemy beasts away at night, by power of the moon, and at day maybe even burn some. If you burn a hole in a dragon's wing, it's going to be flying funny. Also, if you've got telescopes at your tech add a lens, that'll really burn the creatures.

Smoothing the Cracks: If the squirrel things can climb, use melted lead or a equivalent to fill in any spot in the wall, between the bricks, so they can't get any footholds and be able to scale your walls.

Location, Location, Location: If it's possible, build your castle like Helm's Deep from LOTR. Have huge catacombs in the rock. Also here's another idea. If there's a really small mountain, very, very thin at the base, you could do a Minas Tirith (LOTR) style fortress, but looping it all the way around the mountain, and for the dragons, shoot huge nets with boulders attached to them at the dragons, that'll ketch them and pull them to their deaths after a long drop.

Dragon Traps: In the city, have no wooden or grass roofs. Though, make a grass roofed building, and use it as a trap. A dragon can't resist burning things, and they'll go in to burn the building, only to be trapped in a ring of magicians.

Teaching the Common People: Make sure every single person has a weapon, preferably a spear and a sword. Teach everyone how to magically make light, kill things, and a few other helpful spells, and give them little sticks with the runes that they'll need. Have others carving the sticks. Teach people how to fight, and what to do in an emergency. Only have the people walking around the streets in the dead of night, so a dragon won't see them and decided to roast the whole street. Have the people growing mushrooms in the caves and have tanks full of fish. You can also maybe grow some vegetables, so the people don't get scurvy, on top of the roofs and in between houses.

Crossbows: If you follow my mountain idea and they dig deep enough, maybe you'll find some steam vents and the such. Build a water wheel of sorts, and have hundreds of thousands of crossbows, even better, double or triple decker crossbows, they have two or three sets of arms, strings, triggers, and quarrels to fire. Then have this 'steam wheel' power the charging of these crossbows, make them extremely powerful crossbows that would normally take an hour to turn, but with the wheel it takes ten seconds to do a hundred. Then have towers filled with racks of these things. (This plan only works well if your tech has gears.)

Answer 7

The humans are faced with a sizable problem. How to overcome a foe that wants to kill them, isn't to be reasoned with, and can attack from pretty much any location (and direction) in what is probably a couple square miles. People have solved that problem fairly well in other answers. Humans can pave the streets with rune stones, practice defense in depth, and arm every single inhabitant. Other's responses lay out some particularly good specifics there. It is interesting then to consider how the Feralts might try to overcome the humans.

Feralts have several problems of their own. They have access to some pretty great mounts and creatures but none of those creatures live in particularly big packs. Also, the resources creatures that big must consume make them a logistical nightmare to raise in large numbers. Because they can burrow or attack from the sky, hit and run style attacks have some merit assuming there is only so much humans can do to get early warning of attacks. However, Feralts also have a problem because humans have access to magic, engineering, basic chemistry and have no problem presumably attacking the Feralts proactively. Imagine defending yourself against a race that can turn your entire water supply to poison with a single spell any one of them can cast. Feralts probably need to be reclusive, migratory, and engage in hit and run tactics on the cities supply chains. Since it doesn't sound like Feralts can spy on the humans I doubt they would ever directly attack en masse. A single spell or weapon they don't anticipate can just result in all of them dying. That isn't to say one massive unexpected attack might not work, but human's would very likely win any sustained conflict given their advantages.

Answer 8

Something else you might want to consider:

I don't know if your total population number is just anecdotal, but it is crazy high for a fortress on medieval level technology. It's pushing it to imagine them building a structure that 20,000 people could fit into. But if these creatures are a constant threat, they can't just retreat there when attacked, they need to live there. Which means it needs to contain their farmland as well. Some quick math on that:
A quora question discusses how much farmland is needed to feed a person: https://www.quora.com/How-many-people-can-be-fed-year-round-off-of-one-acre-of-crop-growing

The numbers vary, but let's say that your people have managed to get hyper efficient with food choices. Maybe they're vegetarian, since meat is super-inefficient from a land-use perspective. Or maybe their meat is entirely from hunting, maybe they even eat some of these creatures.

We'll give them the benefit of the doubt and say that they manage the more efficient vegetarian number from the list, feeding 4 people per acre. So that's 5000 acres minimum, or almost 8 square miles contained within the fortress, just for farmland. If this is a structure with a roof, it's 1/3 the size of Manhattan, built with medieval technology, yet strong enough to withstand consistent attack from fire breathing creatures.

Not being one to just point out a problem, I have a few suggestions:

1: Cut waaaay back on the population. Like, by an order of magnitude. Presumably, it's the simplest answer, and if the number is just anecdotal to your story, then it has minimal impact. 2-5000 is much easier to maintain and defend for, and you can get a good sized army out of it.

2: half-joking, here: maybe the reason the fortress can withstand it is that the farms are all in outlying country and unprotected, so the creatures much on farmers more often than not. The farmers would rely on the castle/fortress for protection (unreliably) and the knights/lords of the castle would spend as much time enforcing taxes as they do protecting from monsters. This feudalistic system would be a little more in line with medieval times anyway.

3: Add in some non-violent magic components. Medieval technology is not going to get the job done feeding these people, unless there's some serious magical assistance. Maybe it helps them grow food faster (an additional reason for creatures to target them) maybe there are non-violent magical creatures they've domesticated that produce an aura that makes things grow.

4: Combine the thoughts of a few other answers, and place the whole thing in a valley surrounded by inhospitable mountains with interlocking caves and tunnels. This way, your land-based creatures have to go through certain mountain passes which bottleneck the enemy and can be made more defensible with minimal technology and magic. They could even be inaccessible during certain seasons. For the flying creatures, as some have suggested, retreat to the caves. Maybe even have them trick the burrowers into making tunnels and caves in the shape they want, and building parapets and turrets out of the mountain side. If the "fortress" is half man-made, half ideal location, it solves for a lot of your problems of scale while providing additional motive for your creatures.

Answer 9

One world-building point about the architecture of your people: whatever architectural technology they have (stone and mortar, etc.) must be useful on a scale where it can't resist a dragon, before the society would invest the effort in that technology to get it to the point where it could resist a dragon. How did no-technology humans survive to become medieval-technology humans? They ran, they hid, and they lived in high enough numbers that the species survived.

Now that your world has spinterras, your world has an abundance of caves that would be perfect for humans. The caves protect people from the elements, and serve all the functions caves used to serve for early humans. But also, a spinterra cave protects you from dragons. An early human is going to live in spinterra burrows except when they're hunting, to avoid a threat like that.

I'm assuming that either spinterras are a fair bit taller than humans, in which case the burrows would be a nice, memorable setting, or that your world has a normal number of caves, and people are drawn to them for the above reasons. If spinterras are shaped like snakes, and they are human-width or wider, then now you have bolt-holes if the drakons attack which they can't fit through, or passages between places where you can stand and fight.

Now that you're underground, you have a lot more options for your defenses. Once you have magic, you can have traps in the ceiling which drop rocks on your enemies. If drakons can't climb, you can destroy the ground under them. You could even block a tunnel when you're attacked, or suddenly create tunnels into new caves.

Clearly there's some kind of tunnelling magic, since the spinterras have been enchanted with it. Warfare between humans with tunnelling magic would be incredibly fun. Think three-dimensional tactics, traps and ambushes, where enemy soldiers could emerge from beneath your feet at any moment. Now detection becomes important, and subterfuge, illusion magic or magic to make the enemy think they know where you are, so they give away their position by casting.

The spinterras would also be a major threat underground, of course. I think a big part of the defense against them, once humans evolve past "run, hide, hit and hope" would be finding or creating large caverns, and building underground towers. I'm imagining several wooden structures, twenty metres tall, with an enclosed platform supported by four thick wooden stilts at each corner. People in one tower would shoot at the spinterras climbing another tower. The entire village might even be on stilts eventually, with watchers underneath it. The spinterras could (maybe) climb, destroy the stilts, or shoot at the people shooting at them.

Answer 10

You are going to want to build something like Erebor from LOTR. Your best defence is going to be high walls against the land based creatures. Against dragons and such, ballistas will be helpful, but also net launchers. You could fire both nets and chains to ensnare flying creatures. A moat would also be good, because your creatures seem not to like water.

Answer 11

You put nature do the work for you.

The fortress IS INSIDE A MOUNTAIN.

From the "wall" you put defense like @Aify say. If the mountain have a cascade better, it can cool the "wall" against fire and create another layer of defense.

A secondary option for more rural area:

The fortress are small-like mobile towers (or them fly?). Is not that what a tank is :)? This is just for give you a more dynamic setup (because now move into the open is very dangerous).