What to do when conquesting a enemy town?

[Pretorian]

Thanks for the info put here.
When I played with Iberia (great faction to play as I am Portuguese ) I started with some great soldiers (cant remember the name), but after I conquered all territories that in modern days are Portugal and Spain, I coundt build or retrain those soldiers, only some weaker ones.
I then build Mic updates in my southern cities (the ones that could make more units) and still no sign of those great soldiers (they equip in black and have big shields) Is there a manual for every faction so we can know what we need to construct (and in what cities) for making available all our units?
In my capital city Oxtraca, I could only build some weak skirmishers...