How are the sea trade routes determined?

[White Knight2]

During my rome playthruogh I've wondered several times how are the sea trade routes from one port to another determined. The trade route from Ariminium can go all the way to sparta but the trade route from rome only goes to Caralis or Genoa. Is there some criteria to determine these trade route and their maximum limit? For example can't it be possible for trade route from rome to go to Massalia or crotona?

[tungri_centurio]

yea im wondering about that to

[ur-Lord Tedric]

See other answer - funny it should come up twice at the same time.

[White Knight2]

Read your reply on the other post.Thanks for those suggestions.... but one problem I've found is that rome does not get more than two sea trade routes and one of them definitely goes to Caralis, no matter what level of port you build. Why is there a trade route to Caralis when they aren't even trading anything? But what I'm wondering is isn't it possible to increase the maximum length of a sea trade route. For example rome's trade with Massalia can be profitable but I've never seen a trade route between those two.

[Danius]

Read your reply on the other post.Thanks for those suggestions.... but one problem I've found is that rome does not get more than two sea trade routes and one of them definitely goes to Caralis, no matter what level of port you build. Why is there a trade route to Caralis when they aren't even trading anything? But what I'm wondering is isn't it possible to increase the maximum length of a sea trade route. For example rome's trade with Massalia can be profitable but I've never seen a trade route between those two.

This has been a little stone in my boots aswell. Rome is the capital of commerce and yet its merchants only trade with Sardinia.
Looking at the trade fleets in the black sea and eastern mediterranean makes me jealous.