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[Larix]

First of all, as a public service:

The comprehensive guide to using multiple active depots for trading

Don't.


Thank you for reading this public service announcement.

With that out of the way,

I've ended up doing another bit of multiple-depot science recently, unvoluntarily: got yet another caravan gridlock when the humans started leaving the exact moment the third or so dwarven wagon tried to enter the depot. In order to avoid the massive nuisance of a broken wagon - either unloading a ton of shit on me i'd painfully dragged in so the humies would relieve me of it, or showering me with dumb dwarven garbage and preventing any exports this autumn - i bit the bullet and built a second depot because

1. you can untangle caravans by offering an _alternative depot_ and _forbidding the 'original'_. Wagons and especially traders on foot will absolutely not re-path if you don't forbid the first depot they were aiming for.

This worked properly, as per usual. However, there was a slight problem because

2. if any traders have actually arrived at the first depot before you diverted them, they will leave their junk at the old depot. They will not pick it up to bring to the new.

Consequently

3. you'll need to hold two separate trading sessions, one at each depot, if you want to have a chance at all items the caravan brought. You can split the export goods between the two depots, thankfully.

4. You'll need to juggle depot forbiddings to collect and redirect the partial groups. Of note is that traders on foot _always_ path to the oldest unforbidden depot on the map - they will leave a 'younger' depot the moment you unforbid an 'older' one. The oldest unforbidden depot check will happily target unreachable depots: only age and forbidden status are checked, if the oldest depot is unreachable, traders on foot will freeze completely, even in the presence of a dozen reachable depots. Wagons will path to the depot they aimed for and remain there, opening up older depots will not redirect them. They can only be shifted by forbidding the depot they're sitting in (while offering a wagon-viable path to another depot).

Remember that
5. depot default settings are not global, they're defined individually for each depot, which means you'll have to re-set "anyone may trade" on the new depot.

Getting the scatterbrained loonies to trade is only half the battle. The other half is getting them to actually pick their shit up again and not gift you half the garbage you didn't want or sold them.

6. Caravans observe some kind of order in picking up their goods again, probably from first unpacked to last, and presumably stuff they brought onto the map has to go back on the wagon/animal it came from. This means that if the first items unloaded came from a wagon that made it to the older and later blocked depot, you'll need to redirect the entire caravan to the older depot via forbidding the new and re-opening the old, or the caravan will sit around stupidly without even beginning to pick up their goods.

7. Once a caravan has collected all their goods from the depot they're in, they tend to go into full "ready to leave" mode and _may_ fail to pick up the stuff they have in the other depot. I got lucky this time around, after a few days of random standing around in the depot, they made their way to the second depot and cleared it out as well, but i've ended up with half the caravan's stuff on my hands more than once despite my best efforts. This time, i had blocked all exits in hopes of encouraging them to get their belongings instead of running off half-cocked, but they first didn't budge and went to the second depot _after_ i had lowered the exit bridge...
I'm not complaining but am really confused how picking up of stuff in split depots works. Anyway, to finish,

8. remember to demolish your secondary depot. Those things may help avoiding trade failures sometimes, but they misbehave in very strange ways and are just an invitation for follow-up cockups if you don't take them down once they've done their job.

9. Of course, the best approach to double depots is to never ever use them. Double depots are annoying and bug-riddled, the game just doesn't expect multiple depots and handles them very poorly.

[SixOfSpades]

As someone who is planning to have a total of nine depots in the next few years, I can tell I am going to find this quite helpful. Thank you.

(Rationale: I want to make the travel time between edge-of-map and the safety of a depot airlock as short as feasible, and to minimize risk of the arriving dwarves getting tangled up with the exiting humans. My fort is also built on a modular design, with each of the 5 sections able to seal itself off & be completely independent from the others, if need be--naturally, each section must have at least 1 depot of its own. I'm just glad that the arrival of merchants triggers an auto-pause, to allow me to unforbid my choice of depot.)

[Necrisha]

So forbidding all depots won't cause the wagons to bypass your site on pause?

[Larix]

Short answer beforehand: if all depots are forbidden (or if those not forbidden have no wagon access), wagons will bypass you instantly. If there are multiple accessible depots or a mix of accessible and inaccessible depots (only counting those not forbidden!), wagons will spawn alright, but the actual pathing of merchants can get crazy and cause massive headaches when trying to trade and get them off the map again.

Longer answers:
Wagons will only enter the map if "at least" one unforbidden, wagon-accessible depot is present. Ideally, this should be _exactly_ one, because more than one is pretty much guaranteed to result in massive merchant confusion. You can then auto-pause, unforbid your desired depot and forbid the "first stop" depot. You can also have multiple unforbidden depots the moment they come on the map and use the auto-pause to forbid all depots but the one you wish to work with this session. Temporarily forbidding all depots doesn't make wagons vanish and they tend to remain on the map and acquire a new target if offered quickly enough, but i wouldn't rely on it - always make sure one depot is legal at all times (check via "D", it shows number of accessible and allowed depots if there's more than one).

But if all depots start out forbidden or if the allowed depots have no wagon access, wagons will bypass you before you can do anything - i.e. you'll get the "merchants have arrived" and "wagons have bypassed you" messages right with your auto-pause.

One of the obscurer things is that merchants on foot follow different rules - they'll always spawn onto the map, regardless of depot situation, but will always path to the oldest unforbidden depot on the map, regardless of actual accessibility. With more than one depot on the map, this can result in an automatic caravan split between an older depot visited by those on foot and a newer depot visited by the wagons (because it has better or any wagon access). And as i said, the merchants on foot will try to find a path to an oldest depot even if it's completely inaccessible, freezing in place. They can even spawn on a wagon road - but don't go to the wagon-accessible depot, because it's not the oldest. Forbidding the inaccessible oldest depot will un-freeze them.

Merchants will not trade before all of the caravan's goods have been unpacked. If part of the caravan is frozen by bad pathing, the rest of the caravan will refuse to trade. I _think_ you can trade simultaneously at two different occupied depots (as long as any traders are present at the place), but you'll only have access to the goods unloaded at this very depot in each partial session.

In general, to preserve sanity, it's best to make sure only one depot is allowed and fully accessible at any time. Anything else tends to result in bypassing wagons, confused animal handlers and/or inadvertently stolen caravan goods.

To improve caravan safety, the best approach always is to have only one, short and heavily secured, wagon-viable path to the map edge. Wagons will _only_ spawn on map tiles with depot access, unless no such tiles exist or some kinds of biome weirdness interferes. If "legal" wagon-accessible tiles exist, all merchants will spawn on them, wagons, merchants on foot in wagon-containing caravans and elves all alike. If no proper tiles with wagon access are there, merchants will spawn in a largely random location and consist of traders on foot only.

Diplomats don't care about these rules, because they aren't merchants and don't target the depot but your leader. This makes them considerably harder than merchants to draw in safely on troubled maps.

[sirdave79]

Your post describes my experience with multiple depots almost exactly, and youve phrased some stuff id have been woolly describing.

Occasionally multiple depots can be useful. But they take a lot of finangling and my current feeling is that they are not worth the effort. I had the strategy of preventing either the humans or dwarves "landing" wagons on my site suggested and thats the one im currenty going for, to selectively prevent dwarf or human wagons from landing (by closing gates to prevent a path to depot - the foot caravan arrives as normal).

My current embark I have channelled 1 tile in all the way round (Its perfectly flat) apart from 2 3 tile wide gaps. Wagons will only land in those spots.

I have a couple of suggestions relating to these issues that im gonna post in the suggestions.

1) Allow instruments to be "played" at or close to the "site" of a gate. This would simulate the fortress playing trumpets/drums/harps(?) to signal to the incoming merchants their closest path to safety (what they do after that...) This would cause the caravan to repath to that gate, performing a one time/based on dwarf action, repath controllable by the player. This would give a use to instruments (though not a need for large numbers) and alleviate the difficulties of successfully protecting caravans.

2) Caravans should give a realistic estimate of their departure time/packup time. Also an indication of their preferred direction of exit before and when they are leaving will allow one to not have them path round their entire fort if they open the "wrong" gate for them. Possibly also alleviating some head on collisions.

[fractalman]

3. you'll need to hold two separate trading sessions, one at each depot, if you want to have a chance at all items the caravan brought. You can split the export goods between the two depots, thankfully.

I'd be somewhat inclined to deconstruct it...or leave it up, depending on how long the list of items was.  As long as the traders keep at least one piece of luggage trash, you can get the rest of the trash into their wagons.

[SixOfSpades]

In light of recent posts, I shall indeed rethink my strategy.

As someone who is planning to have a total of nine depots in the next few years, I can tell I am going to find this quite helpful. Thank you.

. . .

I'm just glad that the arrival of merchants triggers an auto-pause, to allow me to unforbid my choice of depot forbid the depot that was used for trading last time (& which I've left accessible to the outside), and un-forbid the depot closest to the merchants' actual point of entry (& which is also, not coincidentally, also open to the outside).

[Loci]

After some experimentation, I have implemented a permanent multiple-depot system that functions rather well.

The oldest depot, used exclusively for trading with dwarves, can be built pretty much anywhere. The newer depot, used for trading with the humans and elves, should be built where it can be isolated from your fortress and navigable map edges, and include a "bridge to nowhere" to allow the human caravan to leave the map whenever they choose.

At the beginning of the year (after the previous dwarven caravan has left the map), forbid the oldest depot and ensure that the path is open to the newer depot. The elves are never problematic since they lack poorly-navigating wagons. When the human caravan arrives, trade as usual. After the human caravan has "departed", call your dwarves back to the fortress proper and isolate the newer depot from the fortress and all navigable map edges (the "bridge to nowhere" should remain open). Once the human traders cannot possibly reach the older depot, unforbid it, ensure it has a path to a navigable map edge, and prepare to trade with the dwarves.

Notes:
Do not forbid a depot while there are traders present; doing so will cause them to abandon whatever junk they haven't yet packed.
Do not unforbid the older depot until after the human traders are locked away; doing so may cause the pack animal traders to switch depots, causing various delays and problems.
Do not leave a path from a navigable edge to the newer depot; the dwarf wagons will occasionally choose that depot instead. The "bridge to nowhere" is the only collision-proof exit-only path.


This arrangement completely prevents wagon "accidents" with only a modest investment in setup and light micromanagement.