Locating Ports Adjacent Cities

What are the rules/limitations for how close you can put a port in relation to its city? One thing that I don't like about Venice and Constantinople in the game is that their ports are a good distance from the cities, and can easily be occupied by enemy armies.

I'm wondering if a port can be put right next to a city, so that in the case of Venice/Constantinople, you can't get to the port unless you go through the city.

Another thing I was kicking around was the idea of putting Constantinople's port in such a location that it will block ships from other factions from passing through the Bosphorus... thus representing the strategic nature of the city. It might be too unbalancing, but it's an idea...

You can put a port right next to a city. IIRC I think the second idea has a side-effect of accidental wars starting as the AI bumps their ships into the port. I *think* i had that problem when i tried it in RTW but i don't remember precisely.

Hmmm... I wonder, with Venice, it would be interesting to use that arrangement as well, but put the port facing the mainland, blocking a strait that is the only access to the island. The idea is, this will make it more likely that an AI controlled Venice that keeps a fleet in port will block the strait and make it impossible to attack the city.

This is sort of like the arrangement in EU2, where Venice was only accessible via a strait, and that strait could be blocked easily by the Venetian home fleet. It was an excellent way of preserving the independence of Venice despite its small size and manpower.