On the Structure of the Roman Pantheon

Abstract

Since the time of its construction, the bold, brilliantly simple schema of Hadrian's Pantheon has inspired much emulation, commendation, and even fear. Modern commentators tend to view the building as a high point in an “architectural revolution” brought about mainly through the Roman development of a superior pozzolana concrete that lent itself to the forming of unitary, three-dimensional structures. Other factors cited for the technical success of the Pantheon include the use of a series of massive, concentric stepped rings and the lightening of the dome by coffering and gradated, light-weight aggregates. To investigate these theories, and thereby to understand late Roman design rationale better, a numerical-computer modeling study of the dome structure was undertaken. It yielded several surprises.Analysis revealed that the stepped rings induced higher, rather than lower, critical stresses in an uncracked dome model. But by allowing the model to crack freely, a salutary effect was caused by the rings. The cracked model closely simulated the behavior of the actual dome, which was discerned to act structurally as an array of arches. In fact, the configuration of the dome seems to indicate that the builders understood this which points to the conclusion that late Roman architectural development was not so closely tied to structural innovation as has been generally believed.