Nobody posted this yet? A nice three-page feature on CGSociety which talks with Valve about the TF2 design process in quite some detail. Stuff that is briefly mentioned in the developed commentaries is expanded upon, and it is generally all interesting.
http://features.cgsociety.org/story_cus ... ry_id=4338
[Blocked Image: http://serve.ryanjohnwilliams.com/images/heavy_hair.jpg]
I did a search for 'fortress' and 'tf2' and found nothing on MapCore so if this has already been posted it is entirely your own faults. 
