The purpose of this paper, which is part of a multi-disciplinary research project started in 2018 , is to investigate both the geometry and stability of the dome of the temple of Diana, which partially survived for many centuries. Important observations made by De Angelis d’Ossat  and results of the architectonic survey performed by Rakob  will be presented and discussed; they introduce the delicate issue concerning the identification of the geometric profile of the dome, on which its structural stability depends. It is the Authors’opinion that ascertaining the geometric profile of a dome is not only a matter of measuring, but also of historical context, geometric knowledge and traditions in construction. Thus, by taking all the above issues into account and making use of data from a recent architectonic survey , this paper searches for possible connections with consolidated traditions of the Sassanid architecture imported by the Emperor Alexander Severus, verifies the geometric knowledge presumed to have been acquired by the time of the dome’s construction and identifies the most probable theoretical design: the dome’s meridian profile is a unique curve – to be precise, a parabola, the best approximation of a catenary. Thus, once the profile of the dome has been identified, structural analysis confirms not only the stability of the dome, but also that the Romans were aware of the dome’s behaviour in relation to the construction solutions adopted.
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