Estimating the numbers of residences, and thus the residential densities and populations, of ancient settlements remains a significant problem. This is true even for ‘greenfield’ sites due to the differential visibility of structures made of different materials in aerial and geophysical surveys. In this paper, we take advantage of statistical relationships among elements of the built environments of Roman cities in Britannia and more broadly across the Empire, to estimate the total number of buildings, total population and population density of Silchester. The results indicate that the current site plan dramatically under-represents these values. We also consider the implications of our results for broader discussions of urbanism in Britannia.