when should you build a new fortress?

[Jarkko]

With MA Ulm I think it is *important* to have more forts as fast as possible. Who cares if the capital has fewer resources at use, if you can build a 800 gp fort next to it and recruit an additional smith per turn sooner? More forts = more income and more resources = more smiths (and more knights too).

It is not like early game is too difficult for Ulm ever, is it? But it is so easy to fall behind in the research race as Ulm, and unless you have enough magic to stop the other players, you'll be just a road-bump when you meet another player. Still, it depends on the situation with Ulm too; best is IMO to look for spots with 800 gp forts and start a new one ASAP (as long as it does not mess up the smith producing in the other forts).

With other nations I tend to be much slower with building forts. Usually building first fort in a choke-point and/or something useful to recruit.