Promotions are actually not determined by post count. Senior member is a special rank that is conferred to about 12 people every half year, generally for major contributions to the community.
Pergamon, as stated before, will certainly be a faction. However, team members indicated that Syracuse most likely won't make it. The main problem is that there is barely any information on their military in the post-Alexandrian era. Also, chances are that Syracuse as a faction will end up being simply a speed bump on the way of Rome or Carthage. Archimedes notwithstanding, Syracuses glory days were well and truly over.
Incidentally, the main criteria for faction inclusion in EB are historicity and regional importance. Availability of information is important too, but enjoyability is not a criterion. Now matter how fun it might be, there won't be a Caledonian faction.
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