Watchtower costs?

[Malachus]

Hey guys, I've been playing 0.81a as the Sweboz for a while now and I've noticed that watchtowers cost 2000 while forts cost nothing... is this intentional or a bug?

[MarcusAureliusAntoninus]

Intentional.
Watchtowers are perminent, the cost also includes future upkeep.
Forts would have been realistically built (to some extent) ever time an army set up camp, so they are easier to make.