As in Gold's list, Kothar, Roshad and Mennon are the only civs with what we'd probably identify as a captial proper. 

Roshad doesn't have a central government, as each city is govered by the Patron/Matron/Thinker trio, but there ought to be one 'de facto' city that kicks around more weight than the others. This one, as Gold stated, may act as the main councilhouse for the Thinkers and have the grandest archives and the most renouwned institutions. It may very well be the first of Roshad's cities.

Kothar and Mennon's captials are more traditional, in that they are homes of each nation's king/ruler. These are the jewels of both nations, and it is apparent from their opulence. Both are highly forified, large cities, with vast populations.

We can pull the names out of our asses if need be.