Update - here is a screenshot of the city in question, which is Tuat. I can build a Region 1 government here, and hence a level 5 native barracks. This doesn't really help me though, since I can't train legions etc here, so is only of use economically. Still, any thoughts? There is also a building of "Victory Conditions (Western Greek)" that I cannot destroy, by the way.

Glad to see the forums back up, by the way - thanks to the people who made it happen :)