[DF] defending a fortress from fliers

[Gnome]

The PCs (500-700 point delvers) are about to assault a well-defended human-built fortress. The assaulting party has a caster with Flight-25 who can cast and maintain Flight on the entire party, as well as Missile Shield if need be. He can also create any number of relatively weakish allies with Create Animal. Between the two of them, the PC casters can cast a large number of other relevant spells: Windstorm, Lightning, Concussion, Great Haste, Deflect Missile, and many more. It seems to me likely (but not certain) that they will try an aerial approach, at least if it seems possible to do so.

The defenders should be well-prepared for any sort of attack, including this one or an assault by a large ground force, a small elite force, a dragon, a demon, a mindwarper etc. They have ~100 soldiers (well-equipped and indluding some low-level casters, skills generally around 16) and 5-10 "elite" defenders (warriors with skill levels in the high 20s and casters with skills levels around 20).

So what should the defenders' strategy be? How should the fortress be constructed to be ready to defend against a diverse set of fantasy threats? What kinds of spells/abilities should the defenders have available to make this a challenging encounter? Does anyone have any awesome ideas for fantasy siege weapons that fit well into "DF-world"?
Any other ideas as to how I can make this encounter awesome?

[Anthony]

The standard DF solution to fliers is to put everything important underground, in this thing called a 'Dungeon' :)

[ericthered]

You can also put a roof on everything. It won't be as tough as the vertical walls, but it will help.



The defenders want to force conflicts indoors, if they're up against flying foes.

[The Colonel]

Thin strong wires are also effective against anything making diving attacks - the idea being that they don't see the wire until it's too late to evade, at which point it breaks their wings and they crash and die.
Used by British forces in Aden against scavenging kites that attacked them in camp to steal their food...

[Anthony]

Originally Posted by The Colonel

Thin strong wires are also effective against anything making diving attacks - the idea being that they don't see the wire until it's too late to evade, at which point it breaks their wings and they crash and die.
Used by British forces in Aden against scavenging kites that attacked them in camp to steal their food...

Less useful against flight spells that have no minimum speed and no wings, though midair no mana zones or dispel traps can make life interesting for people using magic flight effects.

[khorboth]

Consider the equivalent of searchlights; a really bright light which can be trained on flyers. Maybe... Roll HT-5 and be blinded for rounds equal to margin of failure. When sight returns, everything except the light source is -5 to target. This will probably be enough time for those on the ground to shoot, cast dispel, position, and do whatever they need to do.

Maybe an illusion only visible from the air? If the defenders aren't powerful enough or don't have enough prep time, it won't be really convincing, but it doesn't really have to be. knowing that it's not an accurate picture doesn't mean you can see what's actually there. So, if it looks like there are no defenders but there really are... then they're hard to target.

The defenders probably have a good idea of what tactically advantageous places to land would be. Those would be great places for traps. Those traps could be ambushes or mechanical or magical or some combination.

If missile shield is a known spell, then it's known that it won't protect against area attacks. Depending upon flight speed, ball lightning can be particularly fun for this application.

What about something designed to make landing areas unattractive? Fake or real patrols, traps, spikes, or archers could force the flyers to land in only a few areas.

Any flying defenders could be accompanied by any number of decoys. A flying fight can be chaotic and anything that makes the attacking force waste resources shooting at illusions or wicker is a bonus.

[Anthony]

Incidentally, large scale mystic mist spells are pretty hilarious for defense.

[David Johnston2]

Originally Posted by Anthony

The standard DF solution to fliers is to put everything important underground, in this thing called a 'Dungeon' :)

Yes. The combination of superior digging ability and the threat from aerial attackers does help explain why the dungeons of dungeon fantasy exist in the first place.

But really if you have a surface installation you want to protect the answer is simple. Anti-air weaponry. Archers and gimbal mounted siege weapons on the walls and towers. And solid roofs on the buildings.

[Gnome]

Originally Posted by Anthony

The standard DF solution to fliers is to put everything important underground, in this thing called a 'Dungeon' :)

Sure, but this fortress is located in a world, and the world includes the possibility of being attacked by an army. Allowing them inside your fortress so you can fight them hand-to-hand seems foolhardy. So there should be some external defenses. But one solution is certainly to make those external defenses easily penetrable by the party so they can get inside and start fighting room to room.

[Anthony]

Originally Posted by David Johnston2

Yes. The combination of superior digging ability and the threat from aerial attackers does help explain why the dungeons of dungeon fantasy exist in the first place.

And in the modern world. Just building DF fortresses in the bunker model is pretty reasonable. The problem is mostly how to combine sensible fortifications with faux-medieval imagery that wants medieval style castles.

Originally Posted by Gnome

Sure, but this fortress is located in a world, and the world includes the possibility of being attacked by an army. Allowing them inside your fortress so you can fight them hand-to-hand seems foolhardy. So there should be some external defenses. But one solution is certainly to make those external defenses easily penetrable by the party so they can get inside and start fighting room to room.

Sure, you put static barriers around your fortress to slow or stop land-based attackers. You just don't rely on them.