You need slightly more than being a ring. It's possible to make a ring (even a field) over R^n provided you don't care about interactions with scalars. For example: Just take any one-to-one map from R^n to R and then apply the operations in R before mapping the results back. It won't make any geometric sense, but it will be a ring.
I've been blanking on what exactly the interactions with scalars that we need to preserve are...
I've been blanking on what exactly the interactions with scalars that we need to preserve are...