In my mod, I have a civ, called mercs, that is located in a heavily warred desert. They are like a crossroads, all roads lead to them. They can only build one unit. It is the "Mercenary" unit. It is immobile, has 0 stats, and is upgradable to a huge chain of other units. I am hoping that I can find a way to have the AI keep its gold and upgrade the unit, but basicly, the merc can be upgraded to different things depending on your tech level. The reason this is really big in my mod is-
Most units, including fighting ones, require food. Mercs do not. They do however, cost an arm and a leg to upgrade. So, you can grow food and make your own units, or through raiding, capturing units, trading and the worx, you can hire mercenaries. (Yeah!)