A new expansion for Crusader Kings II has been announced: Legacy of Rome. In it the player will control the Byzantine Empire, and will have to quell vassal revolts, control scheming generals, and enjoy new Byzantine-specific events and decisions.
New features also include being able to appoint your own Orthodox patriarch, demand levies from vassals, and self-improve your regent with new Self-Improvement ambitions.
The Legacy of Rome expansion is due in Quarter 4 of 2012 through Steam and all other major digital download portals, and should be about $10 USD.
Source: Crusader Kings