The Linked Geometries of the Roman Pantheon and Hadrian’s Serapeum in Tivoli, Part I: The Pantheon

Abstract Building on the strong empirical foundation provided by laser surveying, we demonstrate that the plan of the Roman Pantheon can be generated to high precision by a coherent sequence of geometrical operations, starting from a circle measuring 150 Roman feet in diameter. More specifically, we show that the rotunda design was governed by geometries involving both heptagons and octagons, figures whose relevance are suggested by the 28-fold symmetry of its dome coffering and the eightfold symmetry of its basic ground plan. Related geometries based mostly on the octagon suffice to determine the proportions of the Pantheon’s portico and the placement of its columns. This geometrical analysis can help to shed light not only on the evolving design of the Pantheon itself, but on its relationship to other Roman monuments.