Porsenna's tomb is a monstrous, incommensurable object of wonder that haunted the Western architectural imaginary from the Renaissance to the Enlightenment. Against the backdrop of architecture's interaction with archaeology, this lecture treats various reconstitutions of the fabled Etruscan royal monument. The cryptic description left us by Pliny the Elder (after Varro) prompted architects from Antonio da Sangallo the Younger to Jean-Jacques Lequeu to evoke an impossibly colossal structure premised on the repetitive logic of stacked geometric elements. To take Pliny at his word was to confront the engineering of something that contradicted the Vitruvian mantra of solidity, utility, and beauty. It is arguably with the visionary architects of the late 18th century—and, especially, Étienne-Louis Boullée and his students—that this contradiction found its most emblematic expression. Erika Naginski, professor of architectural history, speculates on why this might have been so, that is, on how it came to be that this ancient megalomaniacal architecture resurfaced in the context of absolutism's demise.