Rome Reborn is a virtual reconstruction of the entire city of ancient Rome at the height of its urban development in 320 AD. The model consists of two kinds of digital reconstructions: Class I elements (whose position, identification, and design are known with great accuracy); and Class II elements (whose building type and location are known only in a general way). Within the Aurelian walls, there are more than 7000 buildings. Of these, ca. 250 fall into Class I, and the rest into Class II. By their very nature, Class I elements can be digitally modeled with a high level of detail and confidence; Class II elements cannot. The challenge in modeling an entire city such as ancient Rome (and, by extension, many other sites known from incomplete archaeological data) is to harmonize the mode of representation of these two classes of buildings. This paper describes how we utilized procedural and parametric modeling techniques to create visually compelling and detailed models of the Class II elements of the digital model of ancient Rome. Procedural modeling methods made the modeling process very efficient without sacrificing detail or quality. Furthermore, the flexibility of the approach helps to quickly change and regenerate the model as new scholarship or discoveries warrant.