In Il Campo Marzio, Piranesi analysed what was then known of the structures and matrixes in this section of ancient Rome. The task was difficult as the Campo had been the most intensely and consistently populated from medieval to contemporary times, and therefore had been the most substantially altered. In the illustrated reconstructions – the Ichnographia and a few bird’s-eye views (Figures 3.1, 3.2 and 3.3) – Piranesi depicted not one single or sustained moment in historical time, such as the Campo under the reign of Hadrian (117-38), but rather a pastiche of times. For example, the Amphitheatre of Statilius Taurus was destroyed in ad 64 and was never rebuilt, and the Horologium Solari Augusti had been in great disrepair for three decades when Pliny (died ad 70) saw it, but Piranesi rendered them in the Ichnographia along with second-century structures created by Hadrian and his successors. Also, it appears that Piranesi invented wildly, an accusation which he anticipated, but one that is not wholly fair, as the methods of archaeological reconstruction were undergoing a seachange even in his day.43
The Pantheon constitutes a central core of a rectangular area comprised of many structures (Figures 3.2 and 3.3). The Campo Agrippa with its many temples and basilicas lies to the front of it, and the Thermae Agrippae (probably begun 25 bc) is to its rear. The area sits in a significant crook in the River Tiber. It is framed by, and in the main on axis with, other major cohesive blocks of monuments in the Campo Marzio. (This axis is most easily identifiable in the Ichnographia in the enclosed complex dedicated to Hadrian of which the Bustum Hadriani is one of the major monuments.) To the zone’s west is an area dominated by the Circus Agonale and the Altar of Mars, said to be the first structure in the Campo Marzio. The Amphitheatre of Statilius Taurus (dedicated ad 29) nestled in the curve of the pavement of the Horologium, forms a distinct unit to its north. To the east, the grid is thrown slightly askew by the Via Lata which feeds into one of the major gates of the Aurelian wall leading into the ancient city proper. A string of buildings including the porticoes of the Septa Julia lines the Via Lata. Finally, the Circus Flaminius (221 bc) is the most distinctive architectonic structure in a rectangular zone to the south. This zone serves as an interface between the rectangular block under consideration and the area which houses two of Rome’s major theatres, that of Marcellus (dedicated 13 bc) and of Pompey (dedicated 55 bc). The positioning of the theatres conforms not to the grid set by the Pantheon and the Campus Agrippae, but to the contours of the Tiber’s bank.
The area in which the Pantheon is a major element is framed by major conduits. The Via Triumphale snakes its way from the northeast corner of the Campo Marzio, across the Tiber via the Ponte Triumphale, and past the western flank of the Altar of Mars. It then proceeds around the southern end of the Baths of Agrippa, moving towards the old Porta Triumphale (shown as closed in the Ichnographia). To the north of the area run the arcades of the Aqua Alexandrina, which encounters the terminus of the Aqua Virgo’s arcades arriving from the east. Their waters service the many structures around the Pantheon, including the Baths of Agrippa and the Baths of Nero (ad 64), also known as of Alexander Severus, for the Emperor who restored them heavily in 227.
The zone reads as a flat and paved area, however, one dotted with numerous trees, and various and varied bodies of water. Rows of trees, including a single line of laurels that runs the length of the Porticus Pollae, mark the southernmost border of Agrippa’s private garden and the northernmost border of the Campus Agrippae. Two fountains adorned with sculpture lay in the area between these trees and the Pantheon’s forecourt. Two rectangular pools of water flank that forecourt. Behind the rotondo is the Horti Agrippae, a public garden donated by Augustus’ general to the popolo Romano for the purpose of vigorous strolling and conversing. Here, the trees are arranged in parterre formation. The large stagnum or exercise pool embraces the garden on three sides.
Surrounding the Pantheon on three sides is a walled and multigated vestibule or courtyard. The enclosing wall creates a space as wide as the rotondo and just slightly longer than the depth of the portico. It bows out slightly at the northern edge. Two cruciform pavilions, one on each side of the portico, are attached to the forecourt. These pavilions are open-air structures that sport porticoes in each arm and serve as elaborate gateways into the court. In them reside the statues of Hadrian and of Trajan, west and east, respectively. These gateways lead to two temple groups, one to each side. In each group there are two peripteral temples, each with a single cella containing three niches on the back wall, a layout typical of Roman temple plans. The cellae face the long lateral side of the Pantheon’s forecourt. The two temples are parallel to each other, and between them lies a rectangular artificial lake. The westernmost temples are dedicated to Trajan and Hadrian, i. e. to two emperors, father and (adopted) son; the easternmost, to Matida and Juturna, i. e. to Hadrian’s mother-in-law, the mother of his wife Sabina, and the ancient goddess of salubrious waters. Attached to the back of each temple group by a lozenge-shaped portico structure is a basilica, rectangular in plan, unusually tall in elevation in comparison to its length and width, topped by a hip roof. Very low structures are attached to the narrower eastern and western fagades of the basilica and create highly enclosed forecourts to the building. The basilicas are dedicated to Matida, on the eastern side of the Pantheon, and to Marciana, Matida’s mother and Trajan’s sister, on the western.
On the north edge of the Campus Agrippae, beyond the temples and the courtyard, is the Porticus Pollae, begun by Agrippa’s sister Vispania Polla and finished by Augustus. This skirts the conduits of the Aqua Alexandrina, beyond which lie the private gardens of Agrippa.
To the rear of the Pantheon is the rich complex of the Thermae Agrippae. The back wall of the rotondo encroaches upon a row of pavilions which line the northern edge of the Horti Agrippae, the rectangular plot of land which Agrippa donated as a garden for public use. Directly behind the rotondo is the Xystus, or vaulted portico (often identified by other scholars as the Basilica of Neptune)44 which extends into the garden. The Stagnum Agrippae, or exercise pool accompanying the Baths of Agrippa, is a near rectangular artificial lake into which the garden protrudes. Two symmetrically placed hemicircular islands rimmed with columns and obelisks inhabit the lake and between them are what appear to be two fixed floating rafts. These islands and rafts provide places for rowers to take temporary respite during their exercise. On the southern bank of the lake lie the main buildings of the Thermae Agrippae. A large central aula, somewhat clover-leafed in plan, is most likely the caldarium, and the symmetrically placed rooms to each side most likely house the tepidarium, the frigidarium, perhaps the laconicum, and some apodyteria.
The building complexes that bookend the Lake of Agrippa are the Thermae of Hadrian to the east, and that of Nero and Alexander Severus to the west.45