Piranesi's Campo Marzio is full of gigantic plans that are on a scale virtually unrealized in actual built architecture. In simple terms, this overuse of size can represent Piranesi's wish to express the grandness of ancient Rome. Beyond that, it is at this point difficult to make any other interpretation. The real issue seems to be that when so many gigantic plans are seen together, the sense of actual scale is lost. The large plans themselves quite naturally are in turn perceived as buildings that are only something like half their actual size. I think this normal misinterpretation of scale is part of the general enigma that the plan of the Campo Marzio conjures up. The plan seems to have multiple layers of unfathomability, and the ambiguity of scale is indeed one of these layers.
The gigantism of Piranesi's Campo Marzio becomes perfectly evident when it is compared with other urban plans at the same scale. I have already done some comparative analysis [97122701 97122702]between the Campo Marzio and parts of Center City Philadelphia, particularly the area around the Philadelphia Museum of Art because that building and the plan of the Benj. Franklin Parkway are themselves, in general, fine examples of an urban design gigantism practiced in America in the early twentieth century. I will have to do more drawings that show greater amounts of area, and I shall perhaps also compose some overlay drawings (meaning superimposed plans).
If anything, this exercise would be a lesson in scale and, in particular, gigantic scale. It could perhaps lead to a better understanding of Piranesi's intention and his ideas on urbanism, and it might also lead to a fine understanding of urban scale in general, where the Campo Marzio may actually shed some light on the urban situation of some actual cities, in this case, Philadelphia.
Piranesi's rendition of Hadrian's tomb fits to scale within Philadelphia's Logan Circle.