By focusing on the material components of this ruin, this image suggests the conjectural re-creation of the substructures of the Anione Vecchio acqueduct. In this print, Piranesi attempts to “spiegare con disegni le proprie idee” (“Lettera Dedicatoria a Nicola Giobbe,” cited in Piranesi 1972, 115, 117).   

Considered together with Piranesi’s index reference to this image, its purpose extends beyond Roman masonry and also makes the argument that these ruins correspond to the substructure of the aqueduct of Anione Vecchio. The image depicts two corresponding ruins and identifies in the center (3) an opening that Piranesi believes to have served as a water channel or canal for the Anione Vecchio aqueduct. Sixtus Julius Frontinus refers to this aqueduct in paragraph 7 of Piranesi’s explanation (and selective translation) of De Aquaeductu Urbis Romae. Although neither Frontinus nor other ancient writers ever make reference to any sort of substructure to the Anione Vecchio aqueduct, Piranesi nonetheless insists that this must be its substructure since the opening, at 25 palmi above ancient ground level, is too high to belong to a sewage tunnel,  and since it could not have belonged to the other waters that flowed in the area (the Appia or a branch of the Augusta) (Index to the Map of Rome, no. 20).  

Piranesi’s attention to Rome’s ancient aqueduct system extends beyond aesthetics and architecture to hypotheses about classical engineering and analysis of the material components used to build these structures. John Pinto observes, “Piranesi’s attention to the material components of Roman architecture was complemented by his parallel interest in its structural dimension, including the engineering and construction techniques employed by the ancients” (Pinto 2012, 105). This print is part of a series in the Antichità Romane that show close-ups of the specific materials used by Roman masons, including “Piece of Tufa,” and “Triangular Stones from the Aurelian Walls.” which examine tufa and tevolozza.   
 
As the third image in this series devoted to building materials and methods, this image appears to showcase the popular peperino stone. The vividly etched lines on the structure establish a contrast between the structure and the sky (to the right of the image) but also between the different building materials used to build the ancient aqueduct. The description specifies that the highest layer of these remains was “fabbricato di peperini, e internato nelle mura urbane” (1). Peperino (peperini, pl.) was a type of grey stone common in Rome and used, as Piranesi states in the Index to the Map of Rome, for the construction of walls, bridge piers, temple columns, voussoirs of ancient theaters, fountainheads of aqueducts, and shrines. It was a grey volcanic tuff, containing fragments of basalt and limestone, with disseminated crystals of augite, mica, magnetite, leucite, and other similar minerals. The name originally referred to dark-colored inclusions in the stone, suggestive of peppercorns. This stone has been used since the Paleolithic era and then, gradually, by the Etruscans for their sarcophagi, by the Romans for public buildings, until it became the dominant building material for medieval and Renaissance buildings. Peperino is an ideal masonry stone as it is very resistant, yet easy to work with. It is one of the most common building materials that Piranesi refers to in the Index to the Map of Rome (referenced 15 times), second only to tevolozza (mentioned 18 times). Although not stated in the description to this print, the water channel of Anione Vecchio (3) appears to have been constructed with tevolozza, a coarser type of brickfilled with opus incertum on the inside. In this image, Piranesi’s attention to the visual features of building materials work together the conjectures he articulates in related texts to convey his argument about Rome’s aqueduct system. (AD)