Thanks for all the quick responses guys, all comments have been helpful

Quote Originally Posted by Coyotemax View Post
10 miles between banks isn't too bad, if there was a landing point at the bend of each, it's not so far from the city that it coulnd't be used as a central location for goods beng shipped overland at that point between the two rivers. (ok, i know there are grammar problems with that sentence, heh)

Depending on how active either of the faults are, that could add some interesting challenges to the region too
This is pretty much what I was thinking. The city is meant to be a parallel to the city of Rome, and is the centre of a similar empire. A distance of say 10 miles between rivers makes it reasonable that settlements would form to take advantage of the proximity between the rivers, and could form a city important enough to form the keystone for a continent-spanning empire.

I also figured that any such formation would be unstable, and as such would require constant human intervention (which would be an understandable endeavor to protect such an important feature).

What sort of landscape would be most reasonable in this situation though? I was thinking a hilly landscape, with the city built on a series of hills that hold the two rivers apart. The city would have initially been two cities, one built on the bank of each river and connected by roads, that have since grown together and become a single entity.