Design for a Chimneypiece with Double Portrait Medallions, and a Seated Figure

Drawing is on verso of a fragment of an etching -- a proof before letters -- of plate 13 of the "Antichita ̉d'Albano e di Castel Gandolfo," 1764, f. 523.
This chimneypiece design includes medallions, a caduceus, and -- as indicated by Piranesi's inscription in the corner -- a fiacola, or torch. Although related to Piranesi's Diverse Maniere, this design does not appear in the plates of that publication. The figure is unrelated to the chimneypiece; it is one of Piranesi's many quick sketches of people seen in the studio, probably just drawn in a blank space on the page, and not intended to be seen as a figure sitting inside the fireplace.