If the ara Martis was the first altar in the campus Martius, the ara Ditis et Proserpinae in Tarento was undoubtedly the second. The springs and pool of the Tarentum naturally suggested an entrance to Hades, and hence the worship of the gods of the lower world was established at this spot. This ara Ditis is said to have been 6 meters beneath the surface of the ground. Upon it were offered sacrifices at the ludi Tarentini, games which were afterwards merged with the Ludi saeculares. The altar of the time of the empire was discovered in 1886-1887, behind the palazzo Cesarini, 5 meters below the level of the Corso Vittorio Emanuale. Two blocks of the altar itself were found, resting upon a pedestal which was approached by three steps. The altar was 3.40 meters square. Behind it was a massive wall of tufa, and round it a triple wall of peperino. Not far away, in a medieval wall, were found large portions of the marble slabs containing the inscriptions which record the celebration of the ludi saeculares by Augustus in 17 B.C. and by Severus in 204 A.D. The altar is not visible, but the inscription is in the Museo delle Terme. (Platner)
Vincenzo Fasolo, "The Campo Marzio of G. B. Piranesi".
On the riverbank, just across the Tiber from the Mausoleum of Hadrian, there is in Piranesi's drawing a depiction of a structure enclosing a crater in the land. It is labeled Terentus occulens aram Ditis et Proserpinae, "the Terentus covering/hiding the alter of Dis and Proserpina." The Terentus was the site of the ludi saeculares, the secular games," held approximately every hundred years. The site of the [GAME]s occludes a means of access to the dark void beneath it. This form a point of connection in "The Eternal City" to a subterranean labyrinth of which the overlying city is an iteration. The en[CRYPT]ed underworld, the world beyond the real, with its sevenfold, labyrinthine geography, is the unknown that can be reached through the known, the city labyrinth above. Piranesi's crater is a Viconian keyhole, a Freudian screen.
"The Key Plan"
"The Key Plan"... ...about the tiny unnamed intercourse building at the end of the axis of life.
...unlocking secrets, gaining access to knowledge.
...the plan as depicting conception, and therefore the intentional starting point for meaning (and hence interpretation as well).
...the symbolism regarding the conception of Romulus and Remus--Mars and the royal Vestal Virgin as the parents.
...the tiny plan as the generator of all the subsequent plans; the beginning of the "embryonic development" of all the other plan formations.
...the signifying effect of inside vs. outside and of solid vs. void.
...the irony that Bloomer's key plan is just across the river and the unfortunate non-starter nature of her interpretation and underworld scenario.
...the connection to the The City of God regarding the fratricide of Romulus towards Remus and its parallel to Cain and Abel.
Generally, Bloomer's treatment of Piranesi's Campo Marzio follows that of Tafuri's, but she investigates some of Piranesi's other work with some originality. She is much better at finding symbolism/hidden meaning in Joyce, however, than she is in finding the same in Piranesi. For her, the (s)crypt(s) signifies a labyrinth (one she often seems lost in herself, even though it is a labyrinth of her own making!). For example, she sees the Campo Marzio plan as representing the labyrinth of the underworld, that place where the [Cartesian] grid/cage of rationality does not apply. Her [s]cryptic efforts getting into this underworld are especially worth reading because it is a thorough aggregate of good research mixed (unfortunately?) with the Tafurian and Derridian agendas (see her treatment of the CM's Terentus occulens aram Ditis et Proserpinae). Inadvertently, however, by going 'underneath' the large plan, she puts all her effort into seeking something that is not there. Essentially, she avoids the real plan itself.
It rocked Eisenman in his chair...
My opinion of Bloomer's book, as far as it relates specifically to reading Piranesi's Ichnographia of the Campo Marzio, is that it is indeed wrong and [somewhat] trite--almost all of what Bloomer writes about the Ichnographia is taken virtually verbatim from Tafuri; she does, however, include some original material relative to the "pit of the underworld" citing it as the entry way into understanding the Ichnographia as a labyrinth, but she misses the real key to the large plan (the tiny intercourse building) which is directly across the Tiber from the pit. Bloomer's book may be fun, but it is not good scholarship in that she really did not come to read and understand the whole plan at all--she went on to seek meaning "underneath" the plan while what she really did was avoid the actual plan itself. Can you honestly say that you now know what the Ichnographia is about after reading Bloomer's book?
Palus Caprae 283b