The paper seeks to find the proper, or at least current, role of theory in Roman archaeology. It sets up a project to study the settlement pattern of Roman Britain from purely material sources and tries to investigate the presence or need for theory in each of the successive steps of the project. A division is found between the gathering of observations and their manipulation, which can be relatively explicit, and the interpretation of the observations which has to have an an element of theory and subjectivity. Three basic questions arise from this title. Which theories? To which areas of Roman archaeology should they be applied? What is the purpose of such application?