This technical paper describes the design and implementation of a game engine for historical massive multiplayer online role-playing games (MMORPGs). We explore the game and system design space with a focus on historical accuracy and provide a detailed discussion of key design goals for the support of a large-scale, distributed and scalable MMORPG. The JominiEngine is a modular and extensible system architecture built on C# and integrates Riak, a non-SQL database, at the core of the persistent data store in order to facilitate scalability. “Overlord”, the first instance of the engine is set in the medieval time period and uses rigorous UML design methodology for both game and system design. In order to enhance the immersive gaming experience, a separate Unity-based client can be used to interact with the game engine.