A long-standing objective for the Lateran Project has been to draw on structural evidence from the Lateran scavi to model the Constantinian Basilica.Lex Bosman has similarly sought to model the structure, initially from observation of the fabric of the standing Archbasilica. This chapter presents the happy outcome of collaboration between these two approaches.Using state-of-the-art visualisation techniques, the authors have brought together the evidence for the interior and exterior appearance of the Constantinian Basilica. The chapter argues that while based on exhaustive research, these 3D models should nevertheless be best understood as ߢprovocationsߣ.Production of these ߢprovocationsߣ is itself an important vehicle for analysis, because it exposes gaps in understanding as each new model drives and is driven by evolving debates about structure, decoration and illumination.