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[Playbahnosh]

I designed a topside fort for my fortress, complete with crossbow towers, moat and drawbridge, then I decided to include a magma-flood pipe, just in case  . Now, the fortifications extend from the mountainside creating a closed space, and let's say the bridge is made of bauxite.

Spoiler: Like this (click to show/hide)

,..,.<-mountain
.,,,________<-walls
,.,.         |_|
,..,,  fort     |
,..,.           ||<-closed drawbridge
.,.,           _|
,.,.______|_|<-tower
.,.,
==== <-magma pipe
..,.,.

(Sorry for the bad rendition)

So, my problem is: when I flood the valley with magma, it seeps through the fortifications. What can I do to have the fortifications so my crossbowdwarves could fire on the enemy, but when all else fails and I need to drown the attackers into molten rock, my fort would be safe on the inside?

I was thinking about building bulkheads (doors) in front of the fortifications and control them via levers, so when I open the death-pipe, I can close the bulkheads like sort of an "iron courtain" to seal off the fort and keep the magma out. But I'm afraid that a door built in front of the fortification (despite of being locked open by lever) will obstruct the view and crossbowdwarves can't shoot at the enemy.

Also, I have doubts about hot steam seeping in.

Any ideas or designs?

[NecroRebel]

Creatures can fire through open doors, though in terms of materials, mechanisms, and labor drawbridges are significantly more efficient.

Also, if you have the shutters on the outside of the fortifications, you'll need something for them to sit on, which can obstruct your marksdwarves' ability to fire downwards somewhat. I can't tell from your picture if your fortifications are on the level above the fortress approach or not. If they aren't, the outside shutters are of course not an issue. If they are, however, I'd recommend putting the shutters inside the fortifications where your marksdwarves would stand while firing.

Like so:

BF++++++++
BF++++++++
BF++++++++

Where the Bs are a drawbridge, the Fs are the fortifications, and the +s are floors where invaders come up or open space over the floors where the invaders come up.

Do note that unless magma flows over drawbridges while they're lowered, they won't deconstruct due to heat, so if you make sure to close the shutters before flooding the valley with magma you don't need magma-safe bridges or mechanisms.

[Diamond]

As the previous poster said, bauxite drawbridges are most efficient. But alternatively, you could use floodgates instead of doors. Either inside of towers, or outside.

[Playbahnosh]

Creatures can fire through open doors, though in terms of materials, mechanisms, and labor drawbridges are significantly more efficient.

I see. But using drawbridges raises (bad pun, heh) other problems.

Also, if you have the shutters on the outside of the fortifications, you'll need something for them to sit on, which can obstruct your marksdwarves' ability to fire downwards somewhat.

Yea, that's what I thought, too.

I can't tell from your picture if your fortifications are on the level above the fortress approach or not.

Both. As I said, I have two arrow towers on the sides of the fort, both extending at least two z-levels up (walls too). I don't know for sure if the magma levels can reach up to the second floor during flooding, so I'll need protection for the upper arrow slits also, and that raises problems.

If they aren't, the outside shutters are of course not an issue. If they are, however, I'd recommend putting the shutters inside the fortifications where your marksdwarves would stand while firing.

If I build the shutters (be it bridges, floodgates or doors) on the inside, what will happen to the dwarf standing on them when I shut them?
....x╬
i...D╬   outside
....x╬
    ^-shutters (x), D = dwarf

Won't they be squished?

Do note that unless magma flows over drawbridges while they're lowered, they won't deconstruct due to heat, so if you make sure to close the shutters before flooding the valley with magma you don't need magma-safe bridges or mechanisms.

I see, so raised bridged actually act like solid walls in regards of magma-vulnerability? That's good to know.

[NecroRebel]

If I build the shutters (be it bridges, floodgates or doors) on the inside, what will happen to the dwarf standing on them when I shut them?
....x╬
i...D╬   outside
....x╬
    ^-shutters (x), D = dwarf

Won't they be squished?

Yes, they'll get atom smashed if you use bridges. Doors or floodgates, however, simply won't close if there's a creature standing on their tile. Which, of course might be even worse since then they won't seal the fort from magma.

I see, so raised bridged actually act like solid walls in regards of magma-vulnerability? That's good to know.

Essentially. More accurately, they don't take magma damage unless the magma is actually in the same tile as them, and since nothing can coexist in the same tile as a raised bridge, they are magma-immune. The same is true of closed doors and floodgates; the magma can't get into the same tile as they, so they take no damage until they're opened.

[nil]

Easiest option is to build an unlevered door on every floor tile adjacent to a fortification, then give them restricted traffic designations.  Dwarves won't walk on them unless they're specifically stationed there, and you won't have to wait for someone to pull the lever (or connect it, for that matter).

[Playbahnosh]

Yes, they'll get atom smashed if you use bridges. Doors or floodgates, however, simply won't close if there's a creature standing on their tile. Which, of course might be even worse since then they won't seal the fort from magma.

Great. So, in case of emergency goblin BBQ, either my marksdwarfs get smashed or the fort is also cooked.

Essentially[...] they are magma-immune.

Cool! Than I don't need to waste precious metals or bauxite.

But the question still stands, how can I seal the fort an emergency (if not from the inside), so my marksdwarves can still fire on the enemy when the threat is low?

Closing from the inside has the disadvantage of killing the marksdwarfs or not working at all, and closing from the outside obstructs view so they can't fire downwards from the tower. Any ideas?

I was thinking about shutters like on real forts, that close downwards, like
       
╬ŻŻ   -> ╬\ -> ╬|    (side view)

is there such a thing in df?

[Dwarf]

Yes, they'll get atom smashed if you use bridges. Doors or floodgates, however, simply won't close if there's a creature standing on their tile. Which, of course might be even worse since then they won't seal the fort from magma.

Great. So, in case of emergency goblin BBQ, either my marksdwarfs get smashed or the fort is also cooked.

Essentially[...] they are magma-immune.

Cool! Than I don't need to waste precious metals or bauxite.

But the question still stands, how can I seal the fort an emergency (if not from the inside), so my marksdwarves can still fire on the enemy when the threat is low?

Closing from the inside has the disadvantage of killing the marksdwarfs or not working at all, and closing from the outside obstructs view so they can't fire downwards from the tower. Any ideas?

I was thinking about shutters like on real forts, that close downwards, like
       
╬ŻŻ   -> ╬\ -> ╬|    (side view)

is there such a thing in df?

No.

[nil]

You could just build a deep trench draining into a chasm or large field right in front of the fortifications.

[Playbahnosh]

You could just build a deep trench draining into a chasm or large field right in front of the fortifications.

I was thinking about it, but I decided against it. There is a large open valley in front of the fort, but that doesn't prevent the magma from reaching the walls since the pipe is near the fort. Right in front of the fort is a moat channeled from the river (for defense and watering/fishing purposes). It surrounds the fort in all sides and provides water for the fortress. Having a magma drain there could, in theory, prevent magma from coming in, but then I lose my aqueduct/fishing area, which is quite bad. Also, it has limited uses, since the drain slowly fills up during repeated scorching of the landscape.

Also, what about steam? Can steam pass through/over the walls of the fort?

[Shade-o]

Steam acts like any other air substance like miasma or mist, so it can move in any direction until it dissipates, and also move through fortifications, bars and grates. It does absolutely nothing, though.

[Reese]

well...

if the fortifications are on a level higher than the area to be flooded, just don't flood high enough for the magma to come in through the fortifications? If the area to be flooded is on an even level with the fortifications, you don't need to shoot down, so you could put raising bridges on the outside of the fortifications, right?

like...

████          ████
  ☺#          #☺_
████    g g   %% █
████░░██████░░██░█

or

████          ████
  ☺#/   g g  \#☺
████░░██████░░████

[Playbahnosh]

Steam acts like any other air substance like miasma or mist, so it can move in any direction until it dissipates, and also move through fortifications, bars and grates. It does absolutely nothing, though.

Aw. I remember playing an older version of DF, where steam could kill stuff, but I see on the wiki, that steam is now harmless. Well, I don't have to worry about that now, but magma can still hurt...

well...

if the fortifications are on a level higher than the area to be flooded, just don't flood high enough for the magma to come in through the shutters? If the area to be flooded is on an even level with the fortifications, you don't need to shoot down, so you could put raising bridges on the outside of the fortifications, right?

Spoiler: like... (click to show/hide)

████          ████
  ☺#          #☺_
████    g g   %% █
████░░██████░░██░█

or

████          ████
  ☺#/   g g  \#☺
████░░██████░░████

Well, not flooding the upper floors can be hard when dealing with a huge, half-map wide BBQ, since for the magma to spread all over, it needs pressure, and with pressure come big, fiery waves that could, and I think will reach the upper levels.

But you answer just gave me an idea. In theory, I could build 10 wide, 3 long drawbridges along the outside of the the walls. When I close them, in theory, they will not only cover the slits on the ground floor, but extend up to 2 z-levels and cover the fortifications on the towers and the walls. I may be mistaken though. Also, this way I'll need a much wider moat, at least 4 wide, so the bridges don't cover it....

[Time Kitten]

I recommend rethinking your distribution system.  Rather than having a multi level wave, have a large reservoir, with a tiny u bend at the bottom for a pump or row of pumps to draw from.  This will give you both a more constant, and a better covering flow.


~~~~███
~~~~███
~~~~███
~~~~███                                                             #☺_
~~~~█ %%           things you want deaded             Gate
~~~~~~█████████████████████████████████

[Playbahnosh]

I recommend rethinking your distribution system.  Rather than having a multi level wave, have a large reservoir, with a tiny u bend at the bottom for a pump or row of pumps to draw from.  This will give you both a more constant, and a better covering flow.

Spoiler (click to show/hide)

~~~~███
~~~~███
~~~~███
~~~~███                                                             #☺_
~~~~█ %%           things you want deaded             Gate
~~~~~~█████████████████████████████████

Well, thanks, it's really something to consider. I used the minimalist design in the emergency BBQ generator, it's essentially a pipe from a magma river leading outside, blocked with a floodgate on the end. I can't really control the flow, it's either set to burninate everything or shut tight. And I'm not sure if pumping will be effective or fast enough when some unexpected major raid or megabeast comes.

To be hones, I stole the idea of the "sea of fire" from the infamous tale of Boatmurdered, but I don't plan on using it as an everyday measure, like I said, just in case. I plan on using the fort for protection, that's why I want to protect if from the burnination, if that happens.

I just had an idea. With some clever pipework, I could channel the lava to flow from the walls, outward, like some form of "greek fire". That way I don't have to worry about the lava coming in, since the pressure will push it away from the walls... at least I hope so...

Also, can anyone confirm, if I build a 3 long bridge, will it extent 2 z-levels up when closed?