Town defenses: what determines if those can be built?

[Slaists]

I think the mechanic is to represent that the fort controls the area around it, and if the attacker wants to proceed he has to take the fort. So when the attacker gets within that range and you choose to intercept, the attacker gets to try and take the fort from you.

hmm...

1) the geography just did not work that way; in order to get to the fort, the enemy would have had to get trough the town (the fort was behind the town, while the enemy was crossing a bridge that ended IN the town).

2) if what you say (about interception) is true, then there should be no chance for the interceptor to "decline".