I picture a murderhole being different in style from a grate or bars. However, these are all similar in nature. A murderhole, to me is a small opening that allows for the dropping of boiling water, oil, etc. or to shoot through. Though, I imagine the liquids being the primary purpose of these murderholes. However, the ideal design for any form of fortification is to maximize the effectiveness of any defender using this fortification while minimizing the potential reprisal from attackers.
In this way do I feel a grate or bars are simply ineffective, as they would most certainly allow more open area to attack through and be seen through than would a typical fortification in the walls of a defensive structure. This would, in my eyes, put a murderhole closely akin to that of a normal fortification tile.
The problem here is that there is no way to currently add murderholes. I think the best way to approach this is to
make a new masonry item be available for construction:
- Floor Fortification (Murderhole).
This construction piece will be able to be placed similarly to any other floor tile (except not on top of solid objects - what would be the point of it then?). It will act akin to any normal fortification, allowing troops to look and fire down, as well as perhaps drop liquids in the future.
Murderholes themselves seem to be primarily for heavy defense. By heavy defense, I mean actually holding a position. It would be difficult to hit anything unless they were directly below you. It's a very limited sight range; even an arrow loop has broader line of sight than a murderhole does. As seen
here, a murderhole is a rather tiny thing. You'd be lucky to hit anything below you while they were moving.
The best bet to actually hit anything by throwing things down murderholes (aside from triggered traps in a hallway) would be to have some sort of barricade, ideally a gate or large door that invaders need to stop in front of and break down in order to get into your fort. While attackers are trying to break through a gate, they are stationary, allowing you to easily drop things down upon them from well-planned murderholes.
The problem here, however, is that siege is currently not an option. Enemies do not stop to try to axe down a door. They do not build rams to try to break down a large door or gate. Murderholes, currently, would have almost no use, seeing as there is no reason for attackers to be stationary under them long enough for you to be firing at them or dropping liquids on them. Until they do, murderholes are pretty much useless.
All you need to do is put a small tower with fortifications on the second floor. Dig a trench around the wall of the tower. Any line-of-sight penalties your dwarves get from being on the second floor -- any blind spots they gained -- will be negated by the a ditch/moat around the base of the tower. Other than that, there seems to be currently no actual reason for murderholes until boiling liquids and siegery is made ready.
Misc:This is the perfect way to implement Stone Fall Traps in the future!Stone fall traps could be rigged to/on murderholes, so that they fall through murderholes from above.
(Edit: Expanded discussion to include usefulness of murderholes in current implementation of DF.)