Okay, let's write this up as a full proposal:
Jomsborg
Primary Effect: all units get +10% combat bonus when attacking cities with a state religion (or boost it to 20%? Not really sure; that seems a bit OP)
OR
Primary Effect: Units get +25% bonus to loot when capturing cities with a state religion (or boost it to 50%? Same issue as above)
OR
Primary Effect: all units produced here get free City Raider I promotions (and City Raider II?)
Great People Points: Great General
Double Production Bonus: either Stone or Furs, depending on whether we use Furs as a required resource
Tech Requirement: Generalship?
(I wanted something early enough that the Vikings could build it shortly after spawn, and 'Generalship' fit the military theme for this wonder -- it's not notable for its construction or appearance, but for the military order that was based there).
Obsolete by: Clergy?
(It was destroyed by the Christian king Magnus the Good during the period when Scandinavia was being Christianized, so Clergy fits)
Other Requirements: Coastal city + 'Pantheon' civic + 'Furs' resource
(Coastal because it's a harbor fortress, Pantheon because it's a military order dedicated to the Norse gods, Furs to geographically restrict it to northern Europe. Though if we do add an early native American civ to the game with the new big map, it'd be hilarious to see this wonder built in early America...)