Name of empire and its capital city

I'm changing the Salakian Empire's name to be more reminiscent of the Roman empire. I know the capital's name translates into, for example, Ardea in the sea. Would the Latin translation be Ardea aikuoris (gen./loc.) or Ardea aikuore (abl.)? If my understanding of Latin is correct, the Empire's new name, keeping with the above example, would be Imperium Ardeís aikuoribus, either way.


Cívis Illústris
A few points:
- You wouldn't use the ablative like that without a preposition.
- aequor is a poetic word. mare is more often used in prose (or, as here, in more general usage).
- Since aequor (or whichever noun you do use) is dependent on Ardea, there is no reason why it would go into the plural.
- You would not put Ardea into the ablative plural after imperium, as far as I know.

As to what the correct form would be:
- I'm no expert in names, and I can't find an exact parallel, but I suspect an adjective (Ardea Maritima) would be more likely than the genitive (Ardea Maris)
- I've only seen imperium in the meaning 'X Empire' in the phrase imperium Rómánum, but I've never seen *Ardeánum (not to mention what to do with the adjective) so I would go with imperium Ardeae Maritimae.
Okay. I'll wait for confirmation before changing anything, but my gut feelings for the locations are below. They reverted the -ae suffix to old Latin's -ai suffix. Also, I used the wrong Ardea (heron, not the city) in the first post.

City: Tíbur Marínum
Empire: imperium Tíburtínum Marínum