This short paper discusses the design of the JominiEngine, a serious game engine for massive multi-player online role-playing games (MMORPG), designed as an educational tool for the learning history. The main design principles of the game engine are accuracy in the historic model, flexibility in the scope of content modeling and cover a wide range of historic periods, cooperative team-play embedded in a competitive game in order to reflect historical context, and high security in the interaction with the underlying game engine.