40d:Fortress defense

You can help your soldiers a great deal by sensible entrance design and use of traps and siege engines. Simple approaches include clustering stone fall traps or cage traps in your entrance. More care is needed when placing ballistas or catapults as they can hurt your dwarves too. Below are some example designs of more elaborate possibilities.

Entrance traps

Fortification Based Entrance Designs

Keep in mind that the entrance to defensive chokepoints should be outside. If you try to set up your defense somewhat underground, ordering your dwarves to stay inside has the result that your carefully designed 'kill zone' will be chock full of your own dwarves at the critical moment.

This particular design works well with plenty of archers, siege engines, and other ranged weaponry.

• + - fortification
•   - pit (filled with spikes, water, magma, whatever you prefer)
• . - Floor
• 1 - Bridge 1 (over pit)
• 2 - Bridge 2 (over pit)
• 3 - Bridge 3 (over pit)
• # - Wall
• r - Your ranged stuff here

   
                  ENTRANCE
######################222######
rrrr+ ................... +rrrr
rrrr+ .               111 +rrrr
rrrr+ .  .   .   .   .... +rrrr
rrrr+ . . . . . . . . ... +rrrr
rrrr+ . . . . . . . . ... +rrrr
rrrr+ . . . . . . . . ... +rrrr
rrrr+  .   .   .   .  ... +rrrr
rrrr+                 ... +rrrr
rrrr+++++++++++++++++ ... +rrrr
rrrrrrrrrrrrrrrrrrrr+ ... +rrrr
rrrrrrrrrrrrrrrrrrrr+ ... +rrrr
rrrrrrrrrrrrrrrrrrrr+ ... +rrrr
rrrrrrrrrrrrrrrrrrrr+ 333 +rrrr

The 3 tile wide lane is for traders, so if you have your trade depot before this, cut it down to a 1 tile lane to slow down invaders more. Retract bridge 1 to force invaders to take the long way, for maximum exposure to your ranged units. Bridges 2 and 3 can be put down to allow more enemies into this pit entrance, then retracted again to trap them again.

The "Inverse Battlement" Design by Sergius

Note that the fortress interior is to the West. The enemy forces come from the East. One by one, they fall as soon as they pass this "bridge" (which is one level above), as the marksdwarves wait in ambush. For extra safety, hollow this tunnel out to the mountain, upwards into the sky (so it counts as "surface" and Dwarfs can "stay inside"). The bridge part can then be made out of construction, as soldiers can be ordered to go outside anyway.

If you're feeling specially nasty, make the tunnel really long into the mountain and build a ballista behind some fortifications. In my current version of the fortress, the goblins have to cross a long series of drawbridges to even get inside the mountain, so the ballista dwarf gets a lot of shots, and I can launch any escaping troops into the air.

Flooded Entrance

Using a chamber as your entrance alongside a chamber full of water and some machinery you can flood or drain the entrance at will.

The basic premise requires two levers, two screw pumps and two gear assemblies. The amount of power required and the number of additional components needed to get the power to the screw pumps varies depending on distance/setup. One pump is placed to draw from chamber 1 and dump into chamber 2. The other is set in reverse. A gear assembly is placed next to each pump and connected to the main power system. Each gear is linked to a lever. Now at the flip of a switch you can submerge your entrance with water or magma for easy, secure defense against creatures that aren't amphibious or magma-dwelling, depending.

The picture above shows the design in action. The green pump is currently on while the red has been disconnected through the grey marked axle. The yellow X is just to mark that there is a channel under the axle.

Siege weapons

One effective way to have seige weapons defend your fortress is:

• . - floor
• # - wall
• s - ballista
• > - Stair
• - channel

        ###########################sss
Entrance...............>     sss...sss
Entrance...............>     sssssssss
Entrance...............>     ssssss...
        ########################sss###

Using this design you can cripple an army using a well timed volley.