I'd be interested to know on what basis the rebelliousness was determined. Did they base it on historical information or for the benefits of gameplay?

Under Roman rule, Britannia can point to the Boudicca revolt, of course, but does that alone warrant the '6' level, and if so shouldn't that be restricted to the Londinium/East Anglia province?

Jerusalem was a hotbed of resistence and Parthia was never really settled by the Romans despite their claims.

But I don't know of any particular issues with the Iberians, the Dalmatian coast or southern Italy (well, not in the ancient period at least).