410 City of God Against the Pagans
The City of God - inverse Ichnographia
I now have a copy of The City of God, and I intend to read whatever parts I feel necessary to make a connection between it and the Ichnographia. Sue Dixon mentioned a specific quotation where there is even a grammatical inversion used to describe the two natures of the city (the earthly vs. the spiritual). What I hope to ultimately demonstrate is that the Ichnographia actually represents both "urban" paradigms; the Ichnographia is a plan of earthly Rome and it is also oppositely/inversely the plan of spiritual Rome. I believe that Piranesi was trying to deliver both messages, meaning he was aware of the two "urban" paradigms and thus used the "planning" of the Campo Marzio to express both.
The connection that is strongest for me is the time-frame of the Arch of Theodosius (the end of the Roman Campo Marzio), the Visigoth siege on Rome, and the subsequent writing of The City of God--all these events occurred within a 40 year time-span. I believe Piranesi was trying to depict, delineate, reconstruct, reenact the inversion from Imperial Rome to the spiritual Rome of the Church. Along with this line of thought there is also the not-so-smooth conversion of Rome from a pagan state to a Christian state.
Now that I am writing this idea down, I see that I cannot really make a big issue of the Ichnographia representing The City of God, but then again, what I am basically saying is that the Ichnographia is neither a archeological reconstruction nor is it a critique of the baroque. (I should collect all the various descriptions of the Campo Marzio with regard to how it has been perceived esp. over the last half century.)
Today, 2.21,98, I see the connection between the Ichnographia and The City of God to be very strong, and, indeed, the basis of the double-theater concept underlying Piranesi's entire design.