Urban VIII and the dilemma of the portico of the Pantheon

In 1625, Pope Urban VIII disassembled and removed the ancient bronze roof truss from the portico of the Pantheon, using the metal to make guns for Castel Sant’Angelo. This ruthless act of spoliation was much criticized at the time, but it also had the effect of shining a spotlight on what had been a neglected feature of the Pantheon’s design. A debate ensued as to the best and most authentic way of restoring the space, some arguing for the construction of masonry vaults, others recommending the use of suspended false vaults or flat ceilings in the portico’s interior. The article presents two manuscript proposals — both written circa 1625–1626 and one of them here attributed to the pope’s doctor Giulio Mancini — in which the structural, archaeological, and theoretical arguments for and against these various solutions are laid out in some detail. Ultimately, though, the problem was one of geometry: the restricted space behind the portico’s pediment imposed severe limitations on what could be built there. The article offers a reconstruction and analysis of the spatial dilemma confronted both by the original architects who devised the bronze roof truss, and by more recent architects — in particular, Borromini and Piranesi — who continued the search for solutions into the seventeenth and eighteenth centuries.