User blog comment:Master Sima Yi/Assassinews 02-08-'12 — Official AnvilNext Trailer/@comment-101.173.42.147-20120803114042/@comment-5266147-20120803123850

they may have been able to add some of the new combat and animations whilst using the old engine, but i think the dynamic weather, rough terrain and increaded npc count couldnt. The game engine is often augmented with aditional engines, more so when older engines are used for new games to add elements not in the original engine eg speedtree used in tes:oblivion for better vegitation. havok is a physics engine used on a number of games, including assassins creed.