[Endoperez]

Forge, as in a place to build equipment, a place for gathering resources, the places where living is easy and where work is available, a place where tools are sold, and food as well, and where markets are established... Place where your people will gather, where they can live, where they can be levied and given proper equipment and put to fight. They're called forts in Dominions.

Now, if you want a forge for improving excisting units... there really isn't a way to do that. The closest thing is the broken armor tag, which is repaired when there are unused resources in a province the units with broken armor are in. Other than that and magic items, restricted to commanders, different equipment would mean different unitand that'd mean making a better-armored version of almost everything.