How can a city protect itself from an invasion of knights riding flying creatures?

Question

I've done a question about Aerial battle of knights riding flying creatures... How would they fight?, that was put [on hold] for being too broad. So I'm splitting the question into a series.

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The context: In my world, we have two cities, each on a high mountaintop, separated by a vast valley. In order to wage war, the warriors of each city bridge the huge gap between them by using flying creatures.

Now, these flying creatures are of various natures... Some are dragon-like pterodactyls, others are giant eagles. But each one can carry only one warrior and his gear. The warriors saddle and mount the beasts like they would do with horses.

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Now, let us imagine that one of the flying armies has indeed won the battle. The army is now flying to the enemy city, in order to drop the knights into the city so as to conquer it. That city has no more flying creatures... so it must use some kind of grounded weapon.

Knowing that their technology is on the medieval level, how could the city defend itself against this menace? Would archers be sufficient or efficient? Would they use catapults, ballistas or any other kind of weapon? And which ammunition would you suggest?

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PS: Links to the other questions for this series:

1. Aerial battle of knights riding flying creatures - preferred weapons for the warriors

2. Aerial battle of knights riding flying creatures - how would their military formations be?

Answer 1

Generally when you lost your entire army the city falls. You never commit your entire army if you can. You'd have a detachment of guards specialized in defending the city.

Regardless, the enemy has won. We lost so many flying mounts they're insignificant to the fight. So what can we still do? We design our city to withstand an arial assault. I assume the mountain isn't flat at the top but a regular mountain.

The city

With access to flying creatures it makes sense your civilization is more vertical then ours have been. Cities got walls to keep people out. It makes sense your people did something similar to the sky. Modern paratroopers and helicopters still need open ground to land.

I imagine your city to be rings of multi-storied buildings. A, your keep, castle, main fortification.
B, Outer wall, reinforced against the keep itself. Your main barrier against the common rabble as well as enemy Knights that entered the city.
C, First ring of buildings. Can be multiple rings easily depending on the size of your city.
D, Outer ring/city wall. Given a land assault isn't mentioned I think you can get away with the outer ring being lightly fortified buildings.
E, Buttresses to support the outer ring. You obviously find them between the rings as well. Can be turned into towers if you wish.

Now you claim your city is on a high mountain top. This will make the weather and specifically snow an issue. So I tried to take that into account. First story entrances and large slanted roofs.

1. Between the rings I envision some sort of wooden covering against the elements. Obviously that would make the city very dark so I think a mixture skylights with canvas or metal grate coverings might work. Maybe even poor glass? As long as it lets light through but somewhat blocks both snow and enemies.
2. Buttress
3. Outer wall of the keep. Has a large roof to keep snow out of the first ring of buildings/the first street. Only open entrance to street level excluding the keep. Can easily be manned with archers and ballistae.
4. Outer wall itself, added buttresses to the keept for additional strength. Has a first story entrancepoint with the first ring of buildings. Probably gates with porticulus.
5. Space underneath the street between rings of buildings. Might be able to turn that into a sewer system.
6. Keep.

What you want is minimize the open space on top so no enemy can simply wander in. Making the keep and it's wall(s) the focus point you create a killzone that's easy to man. The keep should house the barracks and supplies like bolts, arrows etc.

Access between rings is probably archways, gates and tunnels. Anything that's closed at the top. In a sense the city is one large interconnected building. Linked roofs keeping the air closed for snow and Knights. Roofs are likely augmented with metal spikes to dissuased landing there. It's hard to train an animal to go towards danger.

Being tall and thin they would easily stick above the snow. So weather wouldn't make them useless. Might even function like lightning rods, keeping the wooden roofs somewhat safe.

7. High narrow Streets allow for all kinds of cool details. Banners between houses, extra wooden platforms. Etc.
8. Side view of the settlement on the peak.

Weapons

The first thing that came to me was the already mentioned ballista. An oversized bolt in your wing will surely stop any flying animal. Now we want the animals stopped, but this can be done when they're close to the city.

Any fall would disorient our armored Knights that can then be killed by troops on the ground. The perfect weapon for bringing down enemy fliers isn't the heavy ballista, it's the (Chinese) repeating crossbow. Simple design, easy to use but with limited range and power. It can generally go up to 120 meters but effective range is closer to 80 meters. That's little over 250 ft. Now this is completely outclassed by a traditional crossbow in range and power. It struggles against armor of any kind unlike regular crossbows. But wings aren't armored. Wings tend to be quite fragile. The repeating crossbow could fire up to 40 bolts a minute. Now that's a volume of fire you can hit a flying target.

Give regular versions to your guards that patrol the walls. Then mount larger ones near your open areas. Any flier coming close will be showered in bolts. Hit their wings enough and they should go down.

Answer 2

Strategy: Target the enemy mounts close in.

It's unlikely that these cities have one mount for each knight - flying creatures need a lot of space and a lot of food. An invasion force must be very large. So it's likely that the invasion relies upon multiple waves of knights, with mounts shuttling back and forth to carry many knights across.

This sort of attack has several critical weaknesses: The mounts are obvious force multipliers, and so obvious targets. It also means the invasion force is unsupported by infantry. Knights and infantry support each other - either alone is weaker. Knights alone are fairly easy meat to a wealthy and prepared defense of thousands!

So let them land in your kill zones. Target the mounts first, then kill the grounded knights at leisure. The purpose of targeting mounts is to reduce the rate attackers can land, and ultimately to lower the final number of attackers.

Guide the enemy flyers into your kill zones using nets and fire and fortifications and spikes/spears, etc. As each wave of fliers land, puncture as many mounts as possible using crossbows and arbalests and other high-velocity weapons - you want them to fly away fast and scared...and to bleed out on the way home.

Use ordinary barricades and fortifications to channel the grounded knights into separate traps as they leave the landing area. You don't need to kill them - disable them with rocks dropped upon them, tanglefoots, spring-loaded levers, etc. Try to break a leg or arm. Take them out of their armor - it's valuable. Then, still alive, throw them over the edge in full view of their horrified friends above.

Answer 3

Ballistas are the main weapon you would want as their are easier to aim than something like a catapult. You would also want people who can cast magic and items that can cast magic. DnD (Faerun) had bolt casters.

For passive defenses, you want steel cables and/or nets running between towers and spikes on the roofs and tops of walls. You also want your walls and buildings to be relatively tall and close together to make it hard for fliers to get to the ground. make it so there isn't enough room for their wings once they get between buildings.

Towers and walls will have covered platforms instead of open to provide coverage from above.

Also, to prevent the roofs from becoming staging areas for landed troops, give them steep peaks That, combined with the narrow streets and the chains and spikes between buildings will insure that only a few of them make it to the ground in fighting condition.

Answer 4

Your cities were built by people who live with and accept flying mounts as a normal part of life. As such, their access control techniques (such as walls and gates) would be prepared for airborne intruders. For example, perhaps your city is surrounded by an extremely tall wall which rises from the mountain top to above the breathable atmosphere. Flying over the wall would be impossible for medieval equipped knights (or their mounts) so they would have to confront the gates.

Since the gates focus the intruder's access into a smaller, defend-able zone, archers would be very effective at keeping them out.

Answer 5

There are the four ways of trapping and snaring

• mangle
• tangle
• dangle
• strangle

I think that you need to look at tangling up your prey.. causing them to fall out of the sky. Nets are being used currently to disable drones see this net gun. The nets could be launched by ballista and don't need to be heavy, only binding

This could be achieved at night with a ships rigging above the walls, the webbing would have to be difficult to see and supported on multiple points (in case of enmasse assualts)

Answer 6

Spears, lots of spears, set in the ground/rooftops/walls etc. pointing upwards to prevent flying creatures from landing, and/or kill the knights jumping from up high to the ground.

Are balloons with chains, preventing flying creatures to enter airspace over the city out of the question? (like hotairballoons over London during WW2)

Answer 7

An airborne attack has basically 2 means of taking a city.

1. Bomb the city from above using dropped or missile weapons. Rapidly
2. Bypassing perimeter defenses to get troops on the ground.

Bombers

You've said the flying mounts are only strong enough to bear one rider. This means they aren't going to be strong enough to carry heavy bombs like boulders along with the pilot/rider. This means your bombers are going to be limited to standard ranged weapons of the era you are emulating: spears, arrows, bolts, and sling bullets. None of these are going to be particularly effective from a fast-moving flying creature. Shock value? Maybe. But unless they have the numbers to make it rain ammunition, they won't be great at picking off targets. I suppose it is marginally possible that your bombers could light flaming ammunition and drop that to start fires. (Not arrows, though... that's a TV myth.)

These birds/dragons/etc. are going to be large and slow, bred to emphasize power over speed.

The creatures cannot be heavily armored; they lack the wing power for this. And your pilots can only be lightly armored, since they must want to devote as much of their "birds'" power to ammunition. What good is a bomber if it can only carry a pilot and a half-dozen arrows before it has to return home and reload?

To defend against this, your city will build defensive structures with flame-proof, armored, roofs. A stone roof instead of thatched or wooden should suffice. And gives your ground-archers a shield. They sit under that roof, taking pot-shots at anyone dumb enough to fly in range. Give them crossbows if you want a faster ammunition that might have better odds against the bombers. (Maybe a three-person defensive team, the best shooter does the shooting while the other two reload spare crossbows and spot for incoming targets.)

Remember, too, that a bombing force cannot take your city; they can only soften it up by beating it into submission for a ground force or landing air force to then take.

Airborne

Like modern airborne forces (see 101st Airborne Division, US Army), your flying creatures could simply be a means to get men on the ground. These birds will be bred for speed and possibly trained to return to the sally point after their rider leaves. This may allow one bird to supply waves of troops if it survives the flights.

The soldiers will basically be infantry trained to fly into the combat zone. They will carry whatever armor and arms their mounts are capable of carrying, but the speed of landing is vital. While they're in the air, they are larger, vulnerable, targets.

To defend against these airborne troops, you need two things. One, defended archers (see above). And two, restrict your landing areas. If your city has streets too narrow for mounts to land in, then they must land on rooftops or in open parks. It would be a relatively trivial task (assuming the foresight to do so) to build roof lines with points at regular intervals where pole-arms could be set. Imagine a roofline that has weapons similar to these bristling out every three feet or so:

This make the roofs into pincushions where no bird could land. If your mounts are capable of hovering, then troops could jump down onto roofs from the birds, but that still takes some time during when they would be exposed to arrow fire. And you could always throw caltrops out onto rooftops as well, to discourage such efforts.

This limits inbound troops to open park areas. These become killzones where your station defenders with bows, crossbows, spears, etc. Entering that area in the hopes of landing would leave more bodies than fighting men by the end of the day.

An attacking force would probably try to use both Bombers and Airborne troops, but it would be a hard fight in both cases.

Remember, the defenders don't have to kill the birds; they just have to break a wing. And those wings are going to be larger than the body of the bird, so they become easy targets.

Answer 8

Unfortunately, your city should probably surrender (or evacuate, but for reasons that will become clear, that isn't a likely alternative).

Your scenario has two similar mountaintop cities, with similar military technology. Therefore it is logical to assume that both cities employ the various ingenious and excellent defences mentioned in other answers. Unless the commander of the victorious army is a fool (and probably isn't, given that said commander has just secured an overwhelming victory), your final comment:

The army is now flying to the enemy city, in order to drop the knights into the city so as to conquer it.

isn't what will happen 'in reality' - at least not in the way this has been interpreted so far. The army may be flying to the enemy city, but its commander is well aware of the likely defences, even assuming no prior scouting, and won't be landing any troops in kill zones.

Your cities are on mountaintops, which means (a) access routes to the cities are restricted and (b) most if not all food is going to be imported from lowland farms where there is sufficient fertile soil.

Given that the victorious army now has complete air superiority, all its commander need do is lay siege to the city by targeting supply routes. This can be done out of range of many if not all of the city's defences, and will eventually starve the city into surrendering. Should the city have vast food reserves, the victors can simply cut it off - ignore it. The only scenario where they would try to invade the well-defended city would be if that city possessed something the victors needed, and that need was time-limited.

The upshot of this is that neither city would risk losing control of its own airspace, and would not commit to all-out war, but instead defend its supply routes and farms, perhaps with garrisons and way stations that can be rapidly reinforced/resupplied by air.

So, if the cities ~were~ drawn into a 'final battle', the losers probably can't evacuate, without being picked of by patrols of flying knights from the other city, and can either surrender immediately, or starve first and then surrender.

The only way to have the flying army impale itself on the aerial defences suggested is to have either ignorance of these (an invading horde, for example) or sufficient desperation to be willing to incur major losses. Or both.

Answer 9

Simplest method is massed arrow volleys. The most effective would probably be a counter attack with flying mounted warriors of their own.