The place where the bodies of the dead were burned and buried under Hadrian
By its very name, the Bustum Hadriani indicates a place of ritual involving death -- 'bustum' is the Latin for the place where the bodies of the dead were burned and buried. Piranesi integrates the Roman bustum with the Roman tradition of munus, and thus creates an architectural complex that is both bombastic mortuary and public arena.
The Circus of Domitia, which Piranesi situates symmetrically along the axis of Hadrian's Tomb with respect to the Circus of Hadrian, never existed at any time during Rome's history. This circus is one of the Ichnographia's more chimerical buildings, although the name of the circus correctly references the woman whose garden once occupied this location along the Tiber's west bank. Domitia was the sister of Nero's father. "In 59 A.D. Nero caused her to be assassinated, and seizing the gardens, united them to the horti Agrippinae. In building the palazzo di Giustizia, the west boundary of these gardens was found to coincide with the axis of the new structure, and on the west of this line many monumental remains of opus reticulatum and marble were discovered.
It is probable that after the garden of Agrippina and the garden of Domitia were united, the whole park was called the garden of Nero. Before the great changes effected since 1870 in this part of the city, the north portion of this park was represented by the Prati di Castello." (Platner)
Even though the Circus Domitiae is a creation of Piranesi's imagination, he nonetheless lists the building within the Catalogo section of Il Campo Marzio dell'Antica Roma, which is where all the buildings of the ancient Campus Martius are listed along with their ancient textual references:
Circo Apollinare di Domizia «Procopio nel lib. della guerra Gotica.» Furono dissotterrati diciotto anni fa le rovine di questo circo nel sito, ove l'abbiam delineato, ed ove son state dinotate dal Nolli nella sua pianta di Roma moderna. Di esse parla il Fulvio, ove dice: «Vi resta per anco fuori di porta Castello, in quelle vigne vicine, non lungi dalla mole Adriana una piccolo forma di un circo di pietra nera e dura quasi affatto rovinato.» This translates as:
Circus Apollinaris of Domitia «Procopius in his book on the Gothic War.» Eighteen years ago, the ruins of this circus were uncovered (typo in the Italian, either yours or printer's: dissotterrate) at the site where we show it, and where they have been noted by Nolli in his map of modern Rome. Fulvio speaks of them, where he says: "There remains in addition outside the Porta Castello, in the nearby fields, not far from the Mole Adriana [Hadrian's Mausolem] the shape of a small circus in hard black stone, pretty much ruined in fact."
What Piranesi does here is transpose the evidence of the Circus of Hadrian for that of the Circus of Domitia. This is just one of many mistakes throughout the Campo Marzio publication that actually signifies an inversion of the truth rather than an occurrance of factual error. It is as if Piranesi is continually defying his critics in that 'mistakes' can be readily found, but that these inaccuracies are harbingers of further meaningfulness via inversion has heretofore remained unnoticed.