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[darthbob88]

I have two wagon-accessible paths into my fortress; the first path in the north is short and hedged with statues, such that there is only one way a caravan can go, while the second, in the south, is longer and more open, and blocked with a statue so as to be impassable to caravans. Thanks to the one northern path, everything indicates that the trade depots are accessible, with only one safe path in.
According to the wiki, this arrangement should force any incoming caravans to take the northern path, as that's the only accessible path. However, I have twice had caravans bypass my inaccessible site because they didn't believe that my operation was accessible. What am I doing wrong?

[Sphalerite]

Hard to tell from the description.  Can you post a map?

[happydog23]

You don't mention it, but if you use any kind of devices to "seal" your depot,  if you depot is sealed when the traders arrive, the wagons will instantly bypass. 


Also if you did anything like the freestanding door trick, I think that the depot will show accessible, but the wagons will still not come.


Sphalerite is right, if you could provide a map, it would help.

[darthbob88]

Terribly sorry about any quality issues, but here's the northern path.

Spoiler (click to show/hide)

That should give you the idea; there's a few statues on the right side, tight enough to prevent caravans from passing between them, then a channel when it gets too close to the edge to build anything.

And the southern path.

Spoiler (click to show/hide)

Again, not all of the map, but the area between that path and the edges of the map are clear enough to permit wagon travel, aside from the green glass statue smack in the middle of it.

[Sphalerite]

I notice you have a river running through your site.

While I haven't experienced this myself, I have heard that when you have a site straddling a river (as opposed to a brook) you may need to provide caravan access to both sides of the river.  This may be due to the caravan not being considered to have access to the edges of the map on one or the other side of the river.  Try providing a path to the other side of the river and see if that helps.  I can't see any other obvious reason why the path would be considered blocked.

[darthbob88]

I notice you have a river running through your site.

While I haven't experienced this myself, I have heard that when you have a site straddling a river (as opposed to a brook) you may need to provide caravan access to both sides of the river.  This may be due to the caravan not being considered to have access to the edges of the map on one or the other side of the river.  Try providing a path to the other side of the river and see if that helps.  I can't see any other obvious reason why the path would be considered blocked.

I do have access to my site on both sides of the river, plus a bridge across the other dry river. The northern path serves the east side of the river, and the southern side can be accessed from the west side, aside from a bridge across that river outside of my fortress. You can get anywhere on the map without getting your feet wet, and if I removed those statues blocking easy access, you could get a wagon into my fortress from any part of the map, trees aside.

[happydog23]

Try this maybe,

I remember reading somewhere ( and I searched for 5 mins and can't remember what i searched for to find it last time), but when it comes to restricting where wagons, immigrants and traders (animals not wagons), immigrants and non-wagon caravans need a 3x3 place on the map to spawn (actually I don't remember it was a square region greater than 1 tho), while wagons required a 5x5 area to spawn on the map edge. Try making your road a little wider in the north (looks like theres a tree inside the 5x5 area) and see if that helps at all

[Sutremaine]

I've cut off access right down to three tiles using raised bridges and still had them come through. I have a theory -- that I haven't tested and have one piece of anecdotal evidence for -- that wagons have a side of the map that they prefer, or a preferred z-level maybe. There was a topic a while back from someone with your problem, and he(?) solved it by switching his access point to the south side of the map. You'll probably find that while wagons are happy to leave by that path, they won't come in by it.

You know, now that I think about it... the bridge system I had in place was south-entry, and I have a looser setup now that forces wagons to enter on a 30-tile wide strip, but with one entry tile available (due to uncleared boulders). That one's south as well. Coincidence?

[happydog23]

That one's south as well. Coincidence?

I think so... I've had a couple fortresses that I played on Dwarf heaven, and both restricted caravan entrances I made were on the east.  And before I finished restricting it, I've definitely had the wagons come from the west and north.

[Lav]

When the site has a river, only one side (usually the one on which you embarked) will be available for caravans.

So if you try to force caravans to the other side of the river, the game will claim that the depot is accessible, but caravans will refuse to arrive.

Remove some statues from the second road so make it wagon-passable, and the caravans should start using it.

[darthbob88]

When the site has a river, only one side (usually the one on which you embarked) will be available for caravans.

So if you try to force caravans to the other side of the river, the game will claim that the depot is accessible, but caravans will refuse to arrive.

Remove some statues from the second road so make it wagon-passable, and the caravans should start using it.

Shouldn't be necessary; if it's just the side of the river that matters, I should be able to force the caravan to come in from the north if I move the access road from the east side of the river to the west side, since the caravans seem to prefer the southwest side.

[Sutremaine]

Decided to test this properly after reading Lav's post, as it's been bugging me for ages. Used robodwarves to get things done more quickly.

First site: 4x4 cut into four by four rivers / streams, with the points of exit and entry one to a side. Embark was on the lower left quarter of the map.
Second site: 2x2 desert, completely flat.

First site test: Built depot next to starting wagon. Got wagons. Moved to lower right quarter and cut off pathing between there and other quarters completely*. No wagons. Moved to upper right quarter to check if the edges really did have anything to do with it. No wagons. Left depot in upper right quarter and bridged just the upper right quarter and the lower left quarter. Wagons appeared from the lower left quarter. Finished test after that.
Second site test: Built raising bridges against all four edges, leaving a 3-wide bridge on each side for wagon access. Opened top edge, got wagons. Opened right edge, got wagons. Finished test after that.

*To do this I built the bridges on top of walls, the removal of which would cut off the connectivity maps as much as possible. This was a side effect of the construction method, which was in place to stop dwarves from destroying bridges from the wrong side.

Conclusion: If your access-restricted depot should be available to wagons but isn't, then it never will be available.

[happydog23]

Dat there some good science!

This is extremely useful information...  Is it on the wiki anywhere and is it potentially worth a bug report?  I guess who knows if that code even exists int he same form for Df2010 tho

[bluea]

I'd like to propose another test.

With the "sealed desert map", open 1x1 openings on one side, and wagon openings on a different side. Preferably with the "immigrant" openings on the "preferred" side.

I know you can have the wagons and the mules from the same caravan showing up at different points of the same side, but I feel like I've been getting odd results (Wagons bypassed your site type) if the "wagon access" is on a separate side.

[Sutremaine]

Wagon opening on left, immigrant opening on right:

The elves came in by the wagon entrance every time, as did both the dwarven caravan and the pack animals (though they do this even on maps where they can appear anywhere). When I put the trade depot right by the immigrant entrance, some of the pack animals leave by that route. What's more interesting to me is that the liaison appeared for a decade in a row with the wagons. This was unexpected, since they appear even in locations from which they can't reach the fortress. That's not by the wagon connectivity map, which apparently is generated upon embark and then never checked again, but by the normal one which says that two levels connected only by floored-over edge ramps are not actually connected, stupid.

This map might or might not be used by sieges as well. On the one hand, I've had a squad turn up on one of these cut-off areas. On the other hand, I've had them turn up all over the map on another river-split fort. That one did freeze in winter, though, and any map that freezes will be frozen at the start of the year. Perhaps that's another test -- find a map with a river that freezes, and see what depots on either side do. I don't know how this would affect the liaison though. If frozen rivers counted as initial wagon access, there would be a lot of liaisons turning up on the wrong side of rivers.