Trade Routes

[Stoertebeker]

Sorry that I open a thread for such a simple question - but the search option just gives too many hits. I ask myself, how trade routes are handled. It looks simple: Road and/or harbor connection between the capitals. Alright.
But there are several cases, where I just don't understand how the game handles it:

I have the following situation: Me - CivB - CivC. I can trade with CivB, because there's a road. I know, that CivB happily trades with CivC (which I already have discovered) - but I cannot: why? (No one has Navigation or Astronomy so far.)
And how do wars interfere with trade routes?

Could someone post a summary of the conditions that have to be met to establish a trade route?

 

[vmxa]

I pay little attention to trade routes as I do not have many per turn deals. CivB can trade with CivC via coastal access and harbors, where you may not have a coastal connection to CivC. This could be from something as simple as a barb galley parked where it blocks you, while they have another route via say an island.

 

[Boss Tweed]

also, on the topic of how war has an effect on trading...

if you are at war with CivB and your only connection to CivA is through CivB, you will not be able to trade with CivA until an open route is founded. As vmxa said, this could be a barbarian or other enemy units parked on the "choke points"

 

[Lord Emsworth]

I have the following situation: Me - CivB - CivC. I can trade with CivB, because there's a road. I know, that CivB happily trades with CivC (which I already have discovered) - but I cannot: why? (No one has Navigation or Astronomy so far.)

The only thing (apart from hostile units blocking coast tiles) that I could think of at the moment is that CivB has the Great Lighthouse and trades with CivC over sea tiles. I am not sure you could use CivB's GLH abilities.

And how do wars interfere with trade routes?

Both trading partners must be at war with the civ in the middle in order for trade to become impossible. To use your example, You-CivB-CivC, if just you or CivC is at war with CivB then trade should still be possible.


ETA: Now I feel stupid for not thinking of this earlier. You also need to know the map. You cannot trade over un-uncovered coast tiles, for instance.

 

[Stoertebeker]

The only thing (apart from hostile units blocking coast tiles) that I could think of at the moment is that CivB has the Great Lighthouse and trades with CivC over sea tiles. I am not sure you could use CivB's GLH abilities.

It was a Pangea map. There has to be another explanation.

Both trading partners must be at war with the civ in the middle in order for trade to become impossible. To use your example, You-CivB-CivC, if just you or CivC is at war with CivB then trade should still be possible.

Ah, that's good to know!

ETA: Now I feel stupid for not thinking of this earlier. You also need to know the map. You cannot trade over un-uncovered coast tiles, for instance.

Okay, that may be an explaination. Unfortunately, I don't have the save anymore. But following situation: Huge Pangea, the Greeks just to my south. I can trade with them. They trade with Spain (Spain isn't even in the direct neighbourhood of Greece, but they seem to have a sea route). I could also trade with Spain - maybe, because I was lucky and had my early explorers uncovering the tiles where Scandinavia (in between Spain and me) built roads later on?
But I couldn't trade with Korea, located south to the greeks, even if the greeks could ... . Maybe, I should have explored more of the greeks' tiles early on.
So the formula is: Every tile of the trade route should be known by at least one of the trading partners?

 

[Stoertebeker]

I ran some tests: land-routes don't have to be known at all - if there's a road, cities are connected.
Sea-routes have to be known entirely by at least one of the partners (if my partner knows some tiles and I know some, that's not enough. If only my partner knows the whole route, it works).

So, in my example, Greece could trade with Korea, because they knew a sea-route to them, while Korea didn't know it - that's why I could not trade with them.
Spain, on the other hand, knew a sea-route to a greek harbor, so I could also trade with them.
Good to know. If I want early trade options, I should have seafearing opponents.

 

[Lord Emsworth]

I ran some tests: land-routes don't have to be known at all - if there's a road, cities are connected.
Sea-routes have to be known entirely by at least one of the partners (if my partner knows some tiles and I know some, that's not enough. If only my partner knows the whole route, it works).

So, in my example, Greece could trade with Korea, because they knew a sea-route to them, while Korea didn't know it - that's why I could not trade with them.
Spain, on the other hand, knew a sea-route to a greek harbor, so I could also trade with them.
Good to know. If I want early trade options, I should have seafearing opponents.

Good job, thanks.