Defending a kingdom against highly arboreal (6-limbed) enemies

Question

Before getting on to the main topic, I should point out that the defenders and attackers are both the same species, no humans are present in this scenario, as it does not take place on Earth. The race in question is a species of hexapodal, arboreal 'alien.' Comparable to the body plan of a chimpanzee if you were to super-glue an extra set of arms to it.

Because of their evolution in a heavily jungled area, they are extremely proficient in tree-tops (in fact, they're better climbers than they are walkers) and would likely face little trouble scaling a traditional Castle Wall by itself. This alone wouldn't be a large problem for defenders, as they could just drop heavy rocks or tar on top of any would-be attacker, however, their problem comes in the fact that they have six limbs. With (essentially) six 'arms,' an attacker could feasibly scale a defensive wall while protecting their entire body with medium to large shield, pretty much nullifying the previously mentioned gravity-propelled rocks, burning tar, or other on-wall defenses.

Of course, against a highly mobile adversary, the first and most logical defense would be to clear a large area around the kingdom, which forces them to cross an open field so that you could shoot at them from afar, but thinking about after that, what kind of wall, or other effective method could be used to slow down an advancing army? Is there any way to design a wall to stop these types of creatures from getting in, or would such a species skip straight over castle walls entirely?

Answer 1

• You can make walls taller, and with smooth overhangs that they cannot climb
• You can make vegetation gaps, with water/mud obstacles and pit/deadfall obstacles and tanglefoots.
• You can make fire obstacles
• You can tie your defenses into difficult terrain: Mountains and lakes and rivers
• You can create belts of impassable vegetation: Thorny bushes/vines, nettles and other caustic plants.
• An obstacle need not be real - deceptions and fakes can sometimes have the same effect of slowing of channeling.
• Note that obstacles that are not actively maintained and defended are merely minor delays that are generally not worthwhile.

One important purpose of obstacles is to muck with the attacker's plans - to disrupt their plan and their timetable; scramble their units and cause confusion, so key reinforcements show up at the wrong place or time and won't be decisive.

Another purpose is to channel enemy formations into your kill zones, and to keep them there as long as possible: To attrit them so they won't be decisive, or even into ineffectiveness.

Yet another purpose is to slow an enemy advance. Sometimes that provides time to prepare a stronger defense. Sometimes slowing is a strategic goal in itself -- besieging a castle in wintertime (instead of summer) is a great way to throw away an expensive army and lose the war.

Answer 2

Repurposed Arrow Slits

For starts, you can always make it more difficult to climb a castle wall by doing something fun like smearing the side of the wall with pitch or oil. Or, even given six-armed creatures, you heavily sand-down the castle walls to make them incredibly smooth and virtually impossible to climb.

But, if you really want to send people off the wall, the best way to do it is to use arrow-slits. Basically, they're very small holes within the castle wall that archers would use to fire arrows out of. If you took a spear or even just a pole and gave a climber a nice good thrust, you can send them clean off the wall and falling to their (probable) death. Works especially well if they're about sixty feet up. Doesn't matter if they have armor or a shield because you have no interest in stabbing them - just sending them into a death spiral.

Answer 3

Make the wall unclimbable by either one of these options.

1. Make the wall smooth and slippery without any place for the attacker to get a grip. Cover the wall with glass or ceramic material.

2. Make the wall sharp and pointy with spikes, bones, thorns, barbed wire, or pieces of obsidian sticking out of the wall.

3. Build booby traps in the wall like giant chain saws or arrows that shoot out of the wall when the attacker grips certain parts of the wall connected to internal mechanisms.

Or don't build castles. Your fortifications should be first world war style trenches in the open plains. Since you mentioned that the attackers can climb better than they can walk, you can have snipers in the trenches easily shoot at the attackers who will slowly walk through the plains. You can have multiple rows of such trenches. You can also surround the trenches with barbed wire and booby traps to slow down the attackers. If you fill some of the trenches with water the attackers will have to swim, which will also slow them down. You can put water predators such as crocodiles or sharks in the moats.

Answer 4

Simple - just build a 'moat'. i.e. circle your creatures 'tree city' with water if available backed up by of just as good a wide field of open ground of "killing ground' on all sides.You said you creatures don't like walking, how do they feel about swimming?

If water isn't workable a steep ditch with the earth banked up behind it. Shaped so that the forward side i.e. facing the enemy) slopes at say 30 degrees downward while the rear is as close to 90 as you can get. Your attackers can run down into it easily enough but face a steep climb out. And of course the ditch is too long to jump.

In the open field before the moat/ditch you can put dense fields of large, stones embedded in the surface. Neolthic villagers did this. Any enemy charging their walled villages had to suddenly stop and pick their way through the rough ground. Their momentum breaks. You also add pits and traps and a tall thorn hedge - assuming a suitable plant is available. The nastiest toughest plant you can find and prune it to shape.

Behind the ditch is the compacted soil 'wall" making the barrier taller (as per a roman fort) topped with a timber barricade canted outwards at an angle over the ditch well above climbing height. So that even if they climb up they then have work their way over the 'underside' of the wall.

So the order would be open ground, man traps, moat/ditch, earth wall/canted timber fence (perhaps skipping the fence if you have a good thorn wall you can grow instead).

During normal times your citizens can presumably pass back and forth across the open ground using rope bridges or similar. You guard the these like draw bridges and cut them down when needed.