This article details the use of photographic rectification as support for the documentation of the southern facade of the Torre del Pretori (Praetorium Tower) in Tarragona. This Tower was one of the towers that connected different parts of the Provincial Forum. The use of photographic rectification helped us to make a direct analysis into two concepts: the construction processes and the architecture of the building. The documentation permitted various analyses: the characterisation of the building modules, identification of the tools used to work the building materials, etc.