This paper contrasts two different ways to rationalize architecture: as planned structures and as used spaces. The columbarium tombs of Augustan Rome can be used to visualize these two concepts. The construction of subterranean collective tombs presented substantial difficulties that prompted a variety of solutions, depending on the parameters of specific building projects. There is little direct evidence for the planning stage, however, which shifts the focus to the post-construction phase. This phase can be studied in the well-preserved Columbarium 1 in the Vigna Codini, because it features numerous architectural modifications that were sometimes executed long after construction. The gradually changing character of the space reflects evolving tastes, but the extensive retrofitting of outdated structures also produced new conceptual and pragmatic challenges. My conclusion is that the two readings of columbarium tombs explain different structural features and produce different historical narratives that highlight the perspective of tomb builders and tomb users, respectively.