The finite element method (FEM) is currently applied to a wide number of structural design problems including the propagation of fractures in large un-reinforced concrete structures, such as dams. In the present paper I will discuss the applicability of FEM to the static and dynamic analysis of structures in opus caementicium, the results it produces when applied to monumental vaults, and how these results can be used to reconstruct the design philosophy, the historical lineage, and the structural life of these monuments. Where possible, I will draw comparisons with the application of funicular polygons to similar structures. The paper will include examples from structural studies of the Domus Aurea of Nero, the Trajan’s Markets, the frigidaria of the Baths of Caracalla and Diocletian, and the Basilica of Maxentius.