Piranesi, Juvarra, and the Triumphal Bridge tradition

At around this time there were a number of projects for rebuilding the Pons Neronianus, revivals of the project by Julius II to connect the Vatican to the Campo Marzio by way of the Via Giulia and a new bridge to be built on the foundations of the Pons Neronianus. (56) A drawing by Duperac of the Castel Sant'Angelo from the Dyson Perrins Codex, the "remnant of an illustrated manuscript guide to the city of Rome for the Holy Year 1575," (57) shows a project, prompted by the perception that the Ponte Sant'Angelo and Castel Sant'Angelo were flood hazards, to remove the arches of the Ponte Sant'Angelo near the Castel Sant'Angelo and extend the moat around the Castel Sant'Angelo (Fig. 11). This project necessitated the construction of a new bridge on the site of the Pons Neronianus that would feed traffic directly into the Borgo Nuovo. Duperac's drawing shows a gateway on the Vatican side of this bridge (the Campo Marzio side is not visible), which, however, seems to have been prompted less by triumphal imagery th an by the need to suitably pierce a wall lining the Vatican bank.

The maps of Ligorio, Panvinio, and Duperac established the main possibilities subsequently followed. Later maps usually noted a gate on the Vatican end of the bridge, either in the walls or attached to the bridge, and less often, following Ligorio, also one on the Campus Martius end. The name of the gate changes according to the topographical point of view; sometimes it is the Porta Triumphalis, following Panvinio, or the Porta Aurelia, following Ligorio. The way this gate and bridge should be visualized is best indicated by an illustration in Giacomo Lauro's popular compendium of antiquarian images, Antiquae urbis splendor, published in Rome, 1612-28 (Fig. 12), (58) versions of which appeared in guidebooks, such as those by de Rossi and Francois Deseine. (59) Here, following Ligorio, Lauro places a conventional threepassage triumphal arch on the Vatican bank, which is not physically connected to the bridge. The bridge itself seems to be modeled on the Ponte Sisto, enriched with parapet statues.

Early-seventeenth-century opinion, essentially corresponding to Panvinio, is summed up in Antonio Bosio's Roma sotterranea (first published posthumously in 1634) (60) Bosio placed the Porta Trionfale on the Vatican bank of the Tiber, close to the Ponte Trionfale (Pons Neronianus), on the site of the Ospedale di S. Spirito:

The Porta Trionfale, which no longer exists, originally stood in that part of the city where the Ospedale di S. Spirito is found, as the writers on Roman antiquities affirm. It stood almost on the bank of the river, where there was a bridge likewise called "Trionfale" that debouched almost at the gate, the remains of which can be seen today in the middle of the Tiber. (61)

Bosio gives a description of the triumph based on Josephus's account of the triumph of Titus and Vespasian, untroubled by the possibility that the Porta Triumphalis referred to by Josephus was near the Capitol. He makes clear, nevertheless, that the city was entered only after crossing the bridge and, citing Biondo, identifies as the Via Trionfale the route from the Capitol only as far as the temple of Apollo and the site of St. Peter's on the Vatican bank. (62) The name Via Trionfale, he argues, was particularly appropriate for this route since it led to the Vatican cemetery where Saint Peter and his successors were buried. (63) This "closed" reading of the Via Triumphalis would be of some significance for Piranesi, as discussed below.