Free Trade between Civs

[Edward]

Civ3 site
Strategic resources are needed to make certain military units (iron, for example, is needed to make the Swordsman or Roman Legion units)

Civ3 site
Do resources ever run out?
Yes. Though it happens infrequently, resources will sometimes be exhausted, forcing you to find a new source.

Civ3 site
How do I utilize resources?
To access any good, you need to build a road to that good. That good must also be connected to your capitol in some way, be it by road, harbor, or airport. If the good in question lies outside of your borders, you will also need to build a colony on that square. For luxury resources, all cities connected to the trade network will automatically receive the benefit of the luxury. For resources, all networked cities should now be able to build units that require that resource.

It seems to me (and this is just a guess) that you merely have or do not have access to iron (or whatever resource). I think your supply might randomly be exhausted, but I don't think there'll be a fixed number or iron units in the mine, nor will there be a fixed number of iron units per mine that your city/colony can "produce" per turn.

Civ3 siteYou can trade a variety of things, including:

• Gold (lump sum or per turn)
• Resources[/li]

I'm pretty sure you can set up a "give me access to Oil for 3 coins/turn" deal. This (I think) is similar to what Vitmore The Great is referring to when he says "Free Trade" (regardless of what it might mean in the real world). Of course you'll have to pay 3 coins/turn whether you build 100 tanks or no tanks at all. Once you're set your cost, you needn't go back to the Persians every turn and ask that the deal continue. (I assume that you will have to open up the diplomacy screen when you want the deal to stop or to change the price.)

[Edward]

from Civ3.com's 22 Aug Ask the Civ Team update
Finally, another thing to note is that the trade advisor screen will tell which Civ has surplus resources you need, as long as you have a trade route with that civ and are not at war. This allows you to quickly determine who you should be trading with.

Apparently the supplier needs to have a surplus. Perhaps my previous post was incorrect. My next misleading guess is that you need one iron mine to supply yourself with iron. If you have two iron mines then you have a surplus and can supply it to other civs. (perhaps one other civ per "extra" iron mine?)