Quote Originally Posted by Redmeth
The Oppida is the barbarian culture's stone wall. I'm not sure but if as the romans or greeks you take over a barbarian settlement with an oppida an upgrade the town it might transform into that culture's stone wall.
If Vanilla experiences are anything to go by; then you will be able to upgrade the oppidum to Megala Teichea or any such thing and till that time they will remain there as Oppida. (That is if you capture an oppdium, and it gets attacked you will see the oppdium on the battlefield. At least that's what Vanilla Gaulish Stockades used to be like...)