Ubisoft revealed today through its Assassin's Network
website (note: you do need a login to view the site!) that a variation of one of the multiplayer maps, titled "Rome by Night", will be available in Assassin's Creed: Brotherhood (Xbox 360)
once the multiplayer community has amassed 25 million total kills.
If you want to check the overall progress toward unlocking the new map variant, visit the Assassin's Network linked above and click on the "events" link. It doesn't seem like tracking is live just yet as the site is reflecting a zero, but this will be the place to keep track of the community's progress once tracking is up and running.
Between this map reveal and the recently available and recently announced free DLC maps
, it seems pretty clear that Ubisoft is making a great effort to reward those fans that have made the franchise, including its most recent release, so successful.