This paper explores the use of three-dimensional simulations to investigate transformations of urban form in medieval Cairo, and lessons about using computers to support historical visualization. Our first attempt to create a single extremely detailed model of Cairo proved unworkable. From this experience we developed a database approach to  organizing modelling projects of complex urban environments. The database consists of several complete models at different levels of abstraction. This approach has three advantages over the earlier one: the model is never viewed as incomplete, the framework supports both additive and subtractive chronological studies, and finally, the database is viewed as infinitely expandable. Using modelling software as a tool for inquiry into architectural history becomes more feasible with this new approach.