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[Bryan Derksen]

The sieged having an unfair advantage IS true, but allowing the enemy to ignore your efforts isnt the solution. In that case why bother building a fortress at all? Sure it will take time for them to dig to you, but if you dont know they're coming till they pop out under your dining room table whats the difference?

You're making assumptions here about the nature of sapper tunneling that aren't necessarily true, and that I wouldn't expect to be true based on Toady's good work so far. Why would we not know that the sappers are coming? Fortress mode is very light on the fog of war, I would expect to be able to tell where the sappers are digging and where they're likely to come in. I'd have my military waiting for them when they emerge. I think the main point here is that you'd have to _have_ a military, you couldn't just toss up a single constructed wall tile and be safe forever with no further thought to defense.

Fortress design, too, can be done in such a way as to improve anti-tunneler defenses. Don't do something silly like putting your dining hall up against your outer walls. That right there takes care of the "popping out from under tables" problem. If you want to get more elaborate, dig an outer ring of tunnels to allow your military to intercept incoming tunnelers before they reach important stuff - sort of an underground curtain wall. You can even rig the tunnels up with high-pressure water flooders to take care of the sappers remotely.

Pathfinding is a mess not by means of how to make them ignore walls, its more the how do they know where to mine to in the first place(Goblins "knowing" where the armory is without a living soul having ever returned from the fortress is a bit of a stretch), how to limit where theyre allowed to dig out and how much, collapsing strategies, etc. These things can severely reduce performance of the game.

It'll only happen under specific rare circumstances, at particular moments during a siege in progress. I doubt the performance hit will be significant.

[Mckee]

As for the question of how the hell the gobos would know where to tunnel, it's reasonable to assume they would atleast use an educated guess.

If the fortress is in the side of a mountain, with fairly obvious entrance and walls etc A sane person would simply tunnel towards that, until they had a better idea of the layout. Its not going to be exact, and is open to defence plans, which is kind of the point of sieges.

The game already tells us when a siege arrives, why not warn us if they start tunnelling. Its hardly going to doom fortresses, a decent military and some forethought and its not much harder than a conventional siege. Stupid stuff like putting your dinning room and workshops at the edge towards your entrance and likely side of attack isn't going to keep happening with tunnellers. I'd just put some spare rooms/stockpiles or just an empty corridor between the edge and vital stuff.

[Muz]

I'll be honest. I didn't read this whole thread

I'd support tunnelers as a last resort thing. And if it makes sense. I don't want them digging a random ant-hive all over the map. I'd rather they break the walls in the way. Take the shortest path, like the dwarves in Dungeon Keeper did. And make them dig really slowly.

If you want sapping, then make it clear... dig a big zone under the dining room and burn the pillars.

So, I voted yes, assuming it's implemented intelligently. I don't want a solution that the player would just exploit the AI in another way to overcome, though.

[NW_Kohaku]

As for the question of how the hell the gobos would know where to tunnel, it's reasonable to assume they would atleast use an educated guess.

They don't guess, they cheat.  Gobbos and other invaders can already see your own meeting places, and prefer to path to those, using essentially meta-knowledge to try to attack you.

What you'd actually have to start arguing for is to make a system whereby invaders don't cheat.

I don't want a solution that the player would just exploit the AI in another way to overcome, though.

Short of Toady actually creating some sort of self-evolving AI that learns and adapts to the player and starts generating entirely new seige engines to counter player techniques, there is no way that players will ever stop using ways to exploit the AI.  In fact, many players go looking for new exploits just for sport.

[Iden]

It's been ages since i've been in here. But I know I made a number of posts far earlier in the thread. I don't even care to read back through my own, but a quick version of how I feel on tunneling can be summed up again with a few ideas here:

Sieges should have a certain checklist, if you will, of options they have for now creating a path into your fortress. Siege tactics certainly would vary culturally (different civs use different tactics and are more prone to doing certain things than others). Each tactic has a certain chance of being used. The longer you are sieged, the more Fun that could occur. Tunneling should have a small chance to happen, but over time should be more plausible.

If they are looking for a path into your fort and cannot find one, the attackers should randomly select from a list of possible options to create a path. The siegers should then execute an "attack plan". If the attack plan succeeds and a path is opened, they will give up their siege tactic (as it is no longer necessary) and simply attack as they normally would.

If it fails, or the attackers are repelled, they should have the option to re-asses their situation and retreat in order to formulate a new method of attack. Here again, a random # dictating an option from the list of possibilities. A failed attempt should therefore have an even smaller chance of being used again, more likely leading to a new plan of attack.

Digging in, Sapping, Long-Range Missile Attacks, Siege Weapons (transported in, or made of wood, if available), Siege Towers/Ladders, Sneak Attacks (grappling/scaling walls), Waiting (for reinforcements?), Building a Fortified Camp (out of wood, if available), or just simply Giving Up.

The longer the period of time, the number of failed attempts previously made, and how much they hate you all factors into giving a greater chance that the sieging party will just quit the field.

If they tried to dig in and were repelled, they should retreat and try a different method. It is unlikely they would try the same stupid thing twice if it doesn't work.

Also, on the matter of tunneling, the tunnel-making should probably use a pathing script that calculates the least amount of work in a (relatively) straight line towards the general direction of where they think your fort is. It should not be precise. It should be totally possible for siegers to dig in the wrong direction. There should also be a chance that after digging for so long without finding anything that they would just give up and switch tactics. No reason for them to be digging forever and wasting time if they're digging in the wrong direction!

There is also no reason for large tunnels to get a few goblins in. A 1-tile-wide tunnel should suffice. There should also be specific units marked for digging such as Goblin Engineers. That way if you look, you can have plenty warning of what is to come. If they don't have any diggers -- if they don't have the proper tools to dig -- then they aren't going to dig.

Engineers should be necessary for Advanced Sieges. For creating siege weapons and building ladders or towers, for constructing fortifications, or for digging. If you don't have the person to coordinate it, it can't be done. If you don't have the tools, the things can't be built. No siege weapons without an engineer to design and construct it. No siege weapons without trees to provide wood. No siege weapons if there are no axes to cut down trees. No digging if there are no picks or shovels.

[Andeerz]

Iden = win.

Also, http://en.wikipedia.org/wiki/Sapper  :3  Soooo cool. 

Also:http://en.wikipedia.org/wiki/Siege_warfare#Greco-Roman_era has a neat picture for visualization of siege warfare.

Also: From http://en.wikipedia.org/wiki/Mining_(military)

The Greek historian Polybius, in his Histories, gives a graphic account of mining and counter mining at the Roman siege of Ambracia:

    The Aetolians [...] offered a gallant resistance to the assault of the siege artillery and [the Romans], therefore, in despair had recourse to mines and underground tunnels. Having safely secured the central one of their three works, and carefully concealed the shaft with wattle screens, they erected in front of it a covered walk or stoa about two hundred feet long, parallel with the wall; and beginning digging from that, they carried it on unceasingly day and night, working in relays. For a considerable number of days the besieged did not discover them carrying the earth away through the shaft; but when the heap of earth thus brought out became too high to be concealed from those inside the city, the commanders of the besieged garrison set to work vigorously digging a trench inside, parallel to the wall and to the stoa which faced the towers. When the trench was made to the required depth, they next placed in a row along the side of the trench nearest the wall a number of brazen vessels made very thin; and, as they walked along the bottom of the trench past these, they listened for the noise of the digging outside. Having marked the spot indicated by any of these brazen vessels, which were extraordinarily sensitive and vibrated to the sound outside, they began digging from within, at right angles to the trench, another underground tunnel leading under the wall, so calculated as to exactly hit the enemy's tunnel. This was soon accomplished, for the Romans had not only brought their mine up to the wall, but had under-pinned a considerable length of it on either side of their mine; and thus the two parties found themselves face to face.[1]

Those brazen vessels used to detect miners could be used as a rather dwarfy way of telling which direction miners are coming from!  Or, dwarves might naturally have "stonesense" and that could explain the current relatively light fog of war...

[Alastar]

I like the concept in theory, because a foolproof defence is a little easy against many opponents. Opponents digging and/or constructing siege engines would really make my day.

However, I'd want most invaders to be rather poor miners compared to dwarfs, and to have a small 'engineering corps'. Stopping the mining action and turning everything into a conventional siege should be feasible.
Resigning oneself to having one's fortress turned into swiss cheese doesn't sound like fun, and it's justifiable... other civs won't have the same mining tradition, and invaders wouldn't trust themselves to dig without collapsing the tunnel on themselves without any expert around.

[loose nut]

Yeah, I'm fine with tunnelers in a siege as long as they aren't multiple legendaries carving a swath to your dining hall. If they were adequate or competent as I'd expect, it wouldn't be too hard to put counters in place.

On the other hand, some sort of burrowing horror from the deep could plow through stone at considerable speed and cause a lot of damage and that seems appropriate and legend-worthy.

[Beeskee]

I like the idea but there would need to be a reasonable way to counter it.

[Iden]

Yeah, I'm fine with tunnelers in a siege as long as they aren't multiple legendaries carving a swath to your dining hall. If they were adequate or competent as I'd expect, it wouldn't be too hard to put counters in place.

On the other hand, some sort of burrowing horror from the deep could plow through stone at considerable speed and cause a lot of damage and that seems appropriate and legend-worthy.

Exactly. Fun.

And it shouldn't be something that is always used. It should be something that is possible. You should see it happen. But you should not see it happen every siege. Not even every other time. Just every so often someone might try to dig in.

I like the idea but there would need to be a reasonable way to counter it.

There are a few easy solutions to digging. For ease of digging and "pathing", diggers should avoid digging through stone for the most part, unless they are very desperate. They should tend to stick strictly to digging through dirt and sand layers. The harder it is for them to find an easy path into the fort, the less likely it is for them to try to dig in.

Also, as other races should be less experienced in mining culture, they should have a fair chance of "accidentally" digging through damp or warm stone without realizing it. This would expose them to accidentally flooding themselves out.

A few simple defenses.
Moat covering multiple Z-levels: Nothing beats watching some diggers flooding their tunnel.
Magma-moat covering multiple Z-levels: Nothing beats watching some diggers burn in their own tunnels.
Box Corridor anti-wall: Dig out a small corridor the entire way around your fort on multiple Z-levels. If they dig in to your fort, they will hit this corridor. At one point all of these corridors will converge into a small area that leads into an entrance to your fort. With a path into your fort, they will attack. Set traps along the corridors. They will suffer heavy casualties due to traps. When the attackers reach the entrance to your fort, it will be one even bigger trap. Like shooting fish in a barrel.

[NW_Kohaku]

The thing about moats is that you need to set limits on how much they can dig, which has always been one of the things I've responded to against the cry of "don't pansy out and say they can't dig as fast as dwarves" claims...

If they are stopped by a moat 1 z deep, they can just dig 2 z under it... if they are stopped by a moat 3z deep, they just dig 4z under it... if stopped by a moat 10z deep... 20 z deep, 30z deep, etc.  Unless you dig moats down to the magma sea, then unless there is a finite limit on how far they can dig, moats are totally pointless.

And "finite limit" is the ultimate, if exploitable solution, because it means that if they never dig more than 5 tiles deep, any wall at least 6 tiles thick will protect you from all diggers. 

[Iden]

The thing about moats is that you need to set limits on how much they can dig, which has always been one of the things I've responded to against the cry of "don't pansy out and say they can't dig as fast as dwarves" claims...

If they are stopped by a moat 1 z deep, they can just dig 2 z under it... if they are stopped by a moat 3z deep, they just dig 4z under it... if stopped by a moat 10z deep... 20 z deep, 30z deep, etc.  Unless you dig moats down to the magma sea, then unless there is a finite limit on how far they can dig, moats are totally pointless.

And "finite limit" is the ultimate, if exploitable solution, because it means that if they never dig more than 5 tiles deep, any wall at least 6 tiles thick will protect you from all diggers.

As outlined in my previous two posts, I think the best solution would be some sort of pathing script or algorithm that is not concrete, having no "finite limit". However, instead, the willingness to dig (and continue digging), as well as pursue any kind of advanced siege tactic should be determined by other factors. Currently there are a few factors dictating when a siege quits the field and retreats. Adding some sort of indicator on how serious the enemy civilization hates you and how desperate they are to try to keep killing you should be factored on top of this.

Thus a crude value for how much work they are willing to do during the siege. A less serious group will never even bother to initiate advanced siege tactics, while a more serious group will. A group seeking ultimate blood vengeance upon you will perhaps even try multiple advanced siege tactics and won't give up so easily.

Back to Digging. Digging should be pathed in such a manner, as I mentioned previously, that the least amount of work is used to create a tunnel. Any kind of stone should be evaluated as 5x the work as dirt/sand. This will likely translate to a few key points: Firstly, it means they will try to be as close to your fort as possible when digging so that they have the least amount of work to do. The tunnels should try to be a short and narrow as possible. Diggers should also try to avoid digging through stone unless absolutely necessary, and will tire from digging through stone faster than they would in dirt, and give up sooner. This restricts digging, on most occassions, to dirt layers, and will help to limit unnecessary digging and unnecessary tunnel structures that, as people fear, might ruin the map.

Also the pathing should give no precise, concrete path. It should take into account where the diggers are, where their general idea of the fort is, and a lot of randomness. It shouldn't path the shortest path directly into your fort, it should, as best as possible, guess what the easiest area to tunnel would be and try to dig in a direction until discovering your fort or giving up.

The best way I can explain it is that pathing system should give diggers two things:

• Best estimated spot to start digging
• Best direction to dig in

It should be abstract. They should accidentally dig into moats, water, and magma. They should NOT automatically know where things are.

This also helps to prevent the "if they just dig one more z-level down" problem. They don't know how far down they will have to dig, and they're trying to keep the tunnel as small as possible, so they'll just keep digging until they hit the moat. If they hit the moat, then obviously they're going to need to stop. If they do, by some rare chance, detect water, they can try to dig down, but that's more work, and more likely to be stone, and more likely to be discounted.

This also makes it unlikely that deep forts will be dug through very often. It'd be lame if humans breached your fort 27 z-levels below the surface. It's too unconventional. By keeping tunnel pathing minimalist and abstract, Toady could actually do quite a job keeping it from being overpowered, lame, and annoying.

Late Addition:
Sure. This might make tunneling sound underpowered. But how powerful is it supposed to be. It's supposed to try to create a path into your fort. What if you forget to make defenses? What if they build a bridge over a moat and then dig through a few tiles of stone to get into your fort? The moat isn't going to be the end-all of tunneling, necessarily.

One thing that has probably been brought up in the 25 pages of comments here:

If sappers can deconstruct walls, you might want to use walls instead of moats, if you're looking to keep things clean: the sapper won't bother digging under the wall, they'll just make a hole in it, and you can repair it as good as new. If they can't deconstruct walls – or let's say they can't deconstruct metal walls, because they aren't blacksmiths – that could be an (expensive) defense.

Though I am not sure what the appeal of moats is, except cosmetic. If you really want to passively stop sieges, decoy/ bait/ trap tunnels are a much better defense, to the point where it's boring.

When I think of Sapping, I think of this.

I don't think any enemy unit should have the ability to deconstruct a wall. On top of this, no enemy unit should be able to dig through a constructed wall, only dirt/sand or stone. If a wall is to be destroyed, it needs to be destroyed by a Ram, artillery fire, collapsing, or an appropriately flagged enemy.

[loose nut]

One thing that has probably been brought up in the 25 pages of comments here:

If sappers can deconstruct walls, you might want to use walls instead of moats, if you're looking to keep things clean: the sapper won't bother digging under the wall, they'll just make a hole in it, and you can repair it as good as new. If they can't deconstruct walls – or let's say they can't deconstruct metal walls, because they aren't blacksmiths – that could be an (expensive) defense.

Though I am not sure what the appeal of moats is, except cosmetic. If you really want to passively stop sieges, decoy/ bait/ trap tunnels are a much better defense, to the point where it's boring.

[kaijyuu]

Just so long as they can't tunnel into constructed walls made of sturdy materials like metal.

Unless of course they have some sort of siege engine (catapult, trebuchet, ect) or dynamite.

[RAM]

A metal wall is composed of metal blocks, sure, its tough, but not impenetrable...