Why I cannot build mounted units?

[marshall06]

Sorry if this has asked before. I come from a CIV3 background and just start to play CIV4.

I have connected my cities with barrack to a horse resource. Why I cannot build mounted units? I still see that the few mounted units are greyed out inside the city screen .....

Another question. I have read the units can be upgraded like CIV3. But I don't see anywhere mentioned how, or the cost? May I assume that I can do it at barrack like CIV3, with whatever the upgraded cost for that unit?

Thanks in advance.

[Supr49er]

You must discover Animal Husbandry and build a stable on your Horse resource tile and discover The Wheel to build Chariots. You will need to discover Horseback Riding for Horse Archers.

To upgrade a unit, click on it (must be in your territory) and you will see what it can be upgraded to. 'Mouse over' the upgrade unit icon to see the cost.

To upgrade all units of that type, hold down the alt key.

[rah]

It's build a pasture on the horses, and you need archery to build horse archers.

[marshall06]

Thanks guys. It is helpful.

[Willem]

And you don't need to have a unit in a Barracks anymore in order to upgrade it. It can be anywhere within your cultural boundary.

[MoonWolf]

Also, remember that knights require iron in addition to the pets.