I can only assist my previous speaker. Contrary to CAs descriptions sieges formed a large part of 18th century warfare and fortresses were considered very important tools of defence also by the most battle adjunctive persons (Frederic II. of Prussia f. e.). Defence battles should be a bit more easy or, better spoken, a bit more historically correct (because defence is easy if you don't use the forts defence facilities but instead the buildings inside and square up in the middle). No rushes with ropes please. Fortresses should however be more expensive and need longer building time.