A Question of Timing 1: When do Forts come?

[tinkthank]

Anyone know when Forts appear in a turn? Concretely: If I am building a fort and it is due to appear on the next turn, and an enemy force moves into that province on that turn, and I have additionally say 2 commanders on "patrol" and 2 on "research" -- will the battle take place before or after the fort is up? (That is: will everyone except the patrollers take part in the battle or will only the patrollers take part in the battle?)