First, here's the small set I created. Explanation FAR below.
http://www.flickr.com/photos/53963482@N07/sets/72157625163948927/Hello all. I've been playing Dwarf fortress off and on for a few years, but I recently started playing much more after I took a server support position that allows me quite a bit of time where I need to be alert to outside calls, but don't have work all 8 hours. So my fortress is up in the background, and I unpause it when things are slow.
I've always had trouble with the game, given the learning curve, but it kept itching at the back of my brain. So, when the latest release came out, I tried again. I found an awesome place: I'm on a volcano with a sheer cliff and lots of arable FLAT land to the east of the volcano opening. (I no longer have the seed, but I do have an initial save of the world)
Lava is easily accessible, and I went to work. Please note that my FIRST start of this area was when 31 just came out. I've been saving this region for a while, through the releases.
I got ambushed and died. A lot.
So I gave up for a bit until the job I discussed,. After dying more, I finally said, “Why am I digging into the mountain? Screw this, I have a better idea.
I went to the middle of the forest, and dug down, found some rock, and made a nice big enclosure, with several bridges.
I ran out of wood, sent dwarves out for more, got ambushed and wrecked.
Fuck it.
Reloaded again, and dug a channel ALL around the forest, almost right up to the edge of the mountain, leaving a little room in case goblins jump or something. I made a quick stockpile to get everything inside (Lucky there's just silty clay 1 Zlayer down.)
Once all my dwarves and their crap was inside the barrier, I removed all the ramps in the channel, dug back under and walled off my ramp-remover's access point, creating a closed moat.
I then ordered a huge WALL to be built just inside the moat. In the meantime, I went through standard fortress setups. Farms, gathering, bedrooms, workshop setup, etc etc etc. I mined out the magma channels (I call it a magma radiator) for the future magma forge room, and started that up with fortifications in front of the channels, and such. I forget where I learned how to setup a magma forge, but I followed what I believe are standard instructions. That started filling, and I continued work. I created a bridge across the moat wide enough for the traders to pass, and setup the bridge so it created the rest of the wall when it was risen. I then created a winding wall with 2 more bridges for a little more security. I wired up the bridges to levers, and closed the bridge till the first set of traders. I had a mechanic set up stone fall and cage traps, and the wall slowly was built.
After the first traders got in, I opened the bridge, and let them into the depot just inside the first “gate.” A few goblins followed them in, and got killed by the stone falls, or captured in the cages. However, they were, for the most part, killed by the trader guards that were so carefully positioned between the outside and my actual fortress entrance. So I knew I really wasn't that secure. Thus, when the guards left, I closed my bridge again.
The first migrant wave was- nothing. The second and third brought me to about 45, 50. After that, I somehow locked a cat outside, and it triggered an ambush. The next migrant wave arrived, and I kept my bridges locked. I didn't have any decent way of killing the ambushers, so- The migrants died. The 50 dwarves inside just plugged their ears to the screams...
I realized that I needed a way to attack any ambushers from over the wall, and without risking even the possibility of dwarves falling to enemy action. Archers wouldn't be as interesting as the solution I came up with.
I decided to build my first pump stack (I used a single pump to fill the moat earlier) and work with magma. It would be a tremendous effort to finish, and I probably wouldn't need it anymore once it was finished, but I wanted to see what would happen if I created; Well, that in a moment.
Full disclosure: I edited the raws in 2 areas, to allow Gabbro to act as a flux (And let me turn the TONS of iron I had into steel) and to allow me to use clay for glass. I could do everything I wanted to do without glass, or with iron, but I wanted to see what would happen.
My next step, while I began planning for the magma work, was to create more death-certain traps. I created serrated glass blades first, until I read that glass weren't useful in traps. Very well, I'd make them out of steel. While I began laying a framework for a reservoir, and building windmills, I started my steel industry and created piles of steel serrated blades, and surrounded the bridge with weapon traps.
Now that you have the background to getting my fortress to a decent level of “safe,” let me start on my idea of magma-controlled safety. I wanted where I pull a switch and things die, a'la Boatmurdered. However, I had a large area to defend, and the wall I built would make a single point of magma-exit difficult. With that in mind, I decided to create a magma delivery system. I had initially planned on pumping the magma up inside the mountain, making an exit out of the mountain and over the wall and then into either another pump stack, and then to a large (20x20x5) reservoir. From the reservoir, I would then create several “pipes” that go to several points just over the wall, ended with iron floodgates. I'll use a simple control system, using just 4 levers for NESW directions of magma delivery. I also realized that my magma 'radiator' for my magma forge area would be emptied during the filling process of this whole thing, and was able to figure out how to drop a wall on top of the channel I made so long ago, sealing off the 'radiator' and letting me keep those working when I finally start the filling process.
I've uploaded a few of the most applicable images of my fortress. You can see my wall and moat, and the old pump that filled it (I've since taken down the power to the unnecessary pump in favor of sealing the cavern from any possible nasties.)
You should see where I make some tunnels under my little magma moat, and you should see the traps of death by my bridge entrance. As you can see, I probably don't need this magma delivery system anymore; the first siege that arrived ran into the traps and died screaming.
Also, you can see that I've laid the floor of the pipes, and I'm now working on the walls. Next, I'll go the next Z layer up and put down the ceiling, since this system will be under pressure and overflow otherwise. Then, I'll finish my reservoir and begin my filling process.
I'm sure that this has been done before, but I wanted to share what I consider an amusing idea. If this is actually a common defense system I've stumbled upon, please excuse my naivete.