Navigable Rivers?

[Ludens]

I think these rivers were in history used to ship whole armies, others like Euphrat&Tigris, Themse and Loire only in very few cases.

But where these armies shipped in sea ships or in smaller ferries? If the latter, it would be just as well simulated by a ford.

A thought about the trading:

Could it be implemented, that these rivers (and a very small area of coast) belong to Terhazza?
This would allow to use not trading ports but instead markers which give the regions a bonus of trading?

I don't think I quite understand what you are proposing. What would the difference be with the river port building of EB1?