How do you build a fort?

[TBR]

What are the preconditions fo building a fort?

AFAIK you need
-four artillery batteries (used up in building)
-two supply units (used up in building)
-to be in a county with at least 51% military control.

Having all of this met in Frederick,PA (opposite Harper's Ferry) and a Depot already built there, I still can't build a fort.

Questions:

1. Do You need a pre-existing city/town structure as well?

2. Are there any other preconditions to be met (e.g. do the batteries have to be heavy battieries/field batteries/may not be light batteries)?

If 1. is true -> suggestions:

1. Allow fort-building in "empty" counties to give more freedom to the player.

2. If you don't want to do that because you fear the map will be filled with fortresses (even though they are too damn expensive for that to happen), still allow the building of stockades (for a reduced cost, eg. one supply unit) to allow sheltering of units in the winter.

3. To counteract fortress-proliferation if 1. is granted, make the presence of an engineer unit a prerequisite and make the build-time last at least three turns (1,5 months)

[von Beanie]

Rather than repeat it, here's a recent link that answers most of your questions:

http://www.ageod.com/forums/showthread.php?t=4851