errors in "speaking architecture"
...you see a 'building' that is both literally and figuratively conception. This tiny building is indeed one of the few plans within the Ichnographia that Piranesi does not provide with a Latin label, because the building already, through its plan, speaks for itself. It speaks of all the 'concepts' there involved, namely Piranesi's conception of architectural language, and the very conception of Rome [Romulus] itself. Piranesi's architectural intensification here is so tight to the point that indeed the medium is the message.
Essentially, Piranesi designed a building deliniating conception, which also represents Piranesi's conception of the large Campo Marzio plan, which also represents the beginning/conception of Rome itself.