Options when defending a settlement

[Bob the Insane]

RTR has a nice mechanisim in which barracks are replaced/enhanced as culture and political integration buildings (to abstract the control and eventual domination of the conquroring culture)...

So factions of the same culture can use each other's buildings but when the Romans turn up (for instance) they have to start building up their own infrastructure, government and administration. The first level of building gives you a law boost, the second level gives you some access to the cheapest and lightest local troops and so on... You have to progress to the 4th level before you have Romanized the place sufficiently to build Roman style troops there, but once you do you get to build them all (as long as you have the Stables and Archery ranges to support those troop types).