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[Jackzriel]

Today I was playing in a fairly new fortress with a decent part above ground.
I built as to protect me from climbers and then from fliers, I'm not sure if the design was flawed or what but somehow a Titan got into the second floor of my fortress.

The side view of the design of my fortress is the following:

Code: [Select]

   __         Ceiling level
  F___        Titan appearance level
____W         Ground level
Being F-Fortification
        _-Floor (natural or built)
        W-Wall

I don't think something can move diagonally through z-levels  (I didn't built a floor on top of the Fortification).

The titan was attracted to my fort because of dwarves walking next to the fortifications.

Is this a bug, or is my design flawed?

[escondida]

One of these may be your culprit.

[PatrikLundell]

May be covered by the wiki article referenced, but a build fortification has no floor on top and cannot be walked on but does provide access diagonally from above.
It's also been said that walls [or carved fortification, which retains the walkable tile above] without a floor (or other wall, etc...) on top also provides diagonal access, although I've never suffered from that.

[Fleeting Frames]

I don't think something can move diagonally through z-levels

They can, but it's usually encountered with magma sea - one digs an up/down staircase down to the sea, hits warm stone, and stops, but magma crabs climb up in fort through the adjacent invisible magma. I've once seen group of dwarves descending diagonally as well to keep going beating on a troll who was pitted through an unlinked retracting bridge.

Dwarves can move over fortifications to get back in burrow they're defending when pushed out by waterflow as well.

Was your titan flier by any chance? I know they can probably at least jump; there's reports of bronze colossi jumping several z-levels.

[RocheLimit]

Here is how I understand it, albeit based on version 40.24 and before.

When you construct a wall, a floor is included below it but not above it. 
As such, when you construct a wall and then offset a wall above it, it looks like this:

Spoiler (click to show/hide)

While creatures that cannot fly will not path up and over a wall, they can wander-climb it or decide to climb it to reach a visible target. 
With the wall designed as in the previous image, creatures CAN climb through the diagonal gap, as illustrated here:

Spoiler (click to show/hide)

To seal the gap, one needs to construct a floor atop the supporting wall. 

Spoiler (click to show/hide)

Up stairs and ramps also work; not sure about roads.

In pre-df2014 versions only fliers could take advantage of this gap, as climbing and jumping had not been added.  Now, though, any 'hole' in the floor that can be reached diagonally-vertically can be climbed through.  I have run into this problem in multiple forts:

• A fort with a staircase that ended in an up/down stair just above a cavern lake.  Coincidentally, the lake extended to a tile 1 level below and directly next to the final up/down stair.  I did not realize at the time that diagonal movement was possible and that up/down stairs creates a 'hole' in the floor... cave crocodiles loved to path diagonally from the lake into the stair case and eat their fill
• A fort I had in a reanimating biome was going well, with no cavern discovered but an up/down stair case that went down a certain distance and 'ended' revealing solid rock below the final stair.  However, I would occasionally find undead crundles along the path leading from this staircase... but no cavern had been discovered!  After clearing them out, I used dfhack's reveal to show the cavern.  Unknowingly, the staircase had ended just above and left of the cavern roof, four tiles off the ground.  I watched as 200+ undead crundles wandered aimlessly through the cavern... every now and then, one would wander up the wall and slip in through the gap left when the final up/down stair had pierced that floor
• In a 40.24 fort, I had shifted my staircase from one pillar to another in a cavern; naturally I took the time to wall up the sides of the bridge and provide a roof.  I did not floor over the supporting walls for the roof.  A flying forgotten beast came and I zoomed to it, to watch it enter my FB trap.  Instead, it flew up to that covered bridge I had built and moved diagonally into the stair.

I am now very careful to floor over any constructed wall and end every up/down staircase with an up stair.  Hope this helps!

[Fleeting Frames]

Every working example you have ends in (up)-downstairs, which provide a hole below. A constructed downstairs would have left all of those through as well.

Doing a 43.05 test with a cyclops (long-term readers will recognize this as the same cyclops who demonstrated bridges being unclimbable),

 they only escape out to the wider world of sealed area if I build a downstair on the implied floor above constructed wall.


Wide world is a dangerous place, so they got shot immediately, and descended on the outside side.


That said, it's possible the pathing behind this is inconsistent and sight-based(constructed downstairs also allow sight into unrevealed areas, for dwarven eyes only).

However, I can also cite a counterexample where one could tunnel through constructed floor: By Sanctume

[RocheLimit]

Curious, I just did my own test; embarked in 43.05 randomly with 30 blocks or so and had them build a 4x4 enclosure.  After sealing it with a roof & leaving two wall-tops uncovered, I revealed the circus and teleported a clown up.

And you're right; he stayed right where he was.  Even after building down stairs on the two empty tiles, he did not react.  Of course, he did maul one of the starting seven that happened to walk over those down stairs, but he's not climbing out.

Spoiler (click to show/hide)

*edit: further, removing the stairs and then placing a dwarf on the same tile where the first was eviscerated, with the clown in the same spot as before, did not lead to further evisceration.

Spoiler (click to show/hide)

I guess my third anecdotal story, where a fb slips between the top of a wall and a floor, can only be attributed to the fact that it was flying, not climbing.  Still... with your example down stairs were needed for a successful escape.  Downstairs, as mentioned, provide a hole down below.  Which implies said hole did not exist before the downstair was built.  How, then, can fliers pull the trick off if there is no hole?

[Fleeting Frames]

Build a workshop nearby, to add a new building for buildingdestroyer to trap to? Use liquids to push him around a bit to shake his pathing?

I dunno precisely how keas could tunnel through constructed floors for Sanctume either, my speculation is that flying's 26-tile pathing options don't check if there's a path from 1 tile to another, since there's normally never a walkable path from 1 air tile to another. It's hardly perfect, though.

[Eater of Vermin]

Hmm...  so would I be correct in assuming that the following design isn't 'safe' either?

Code: [Select]

../WWW    / = ramp 
..F_..    W = block wall
...W..    F= carved fortification in block wall
...W..    _ = contructed floor
GGGGGG    G = Ground
Access can be gained diagonally down from the outside ramp to the internal floor?  (I like to place ramps on fortif's purely 'cos they look nice in 3D-visualisers.    )

[PatrikLundell]

A ramp ought to work the same way as a floor in this regard, and should be safe.

[Loci]

Downstairs, as mentioned, provide a hole down below.  Which implies said hole did not exist before the downstair was built.  How, then, can fliers pull the trick off if there is no hole?

Anything that "overrides" the implied floor with a non-floor works, like tree branches.