Abstract
Giovanni Battista Piranesi, well-known as a great engraver, produced at least six schemes to restore the Presbiterio for San Giovanni in Laterano. This paper deals with a "colonnato" planned in the third proposal (Tavola Sesta), then suggests that it be related to Filippo Juvarra's grand project for il Duomo di Torino under the general recognition of Palladio's influence on both architects. Piranesi, in particular, must have referred to a plan of the Quarto Progetto for the Duomo when he faced Borromini's Lateran nave which Juvarra had also traced in the drawing titled Pensieri per la navata del Duomo di Torino.