In Plate III, for the first time, we find ourselves in a completely interior space with no visible exit. Nonetheless, the architecture gives us hints that we are still at the top of what will be a long voyage into the entrails of Piranesi's underground. At the top of the illustration, the groin vaulted ceilings indicate there are no upper spaces to go, but only an indeterminable descent. Also in this plate, we can see the debut of Piranesi's port-like structures including, in this etching, the round tower and the sentry boxes. It's also in this plate that a recurrent image in the series appears for the first time: the people hanging cloths on the parapet of catwalks.
Most of the illustrations of the