As an architectural rendering, this image depicts the only extant ancient four-way arch in Rome. The triumphal arch held particular significance for Piranesi: it is a distinctly Roman form, and he indeed uses such a structure to suggest “the essence of Roman antiquities” in this volume’s frontispiece (Kantor-Kazovsky 68). This four-way arch was, as Piranesi’s title indicates, one of two such arches that Lucius Stertinius, a proconsul in a region of the Roman empire in what is now Spain, had constructed in the Foro Boario (after returning to Rome c. 196 BCE). Wispy vegetation descends from the top of what was used as a tower towards two levels of niches in the arch’s piers. At the base of the left pier, Piranesi’s stone slab caption bears the image title and two small fissures. With the language and appearance of this caption and the integration of information in this image, Piranesi emphasizes the distance of Rome’s ancient past and embeds that temporal distance in the design of this volume. 

Carolyn Yerkes and Heather Hyde Minor have demonstrated that Piranesi, long seen as a maker of individual prints, was fundamentally a maker of books for whom the page, rather than the individual print, was the “primary artistic medium” (Yerkes and Minor 27). As an informative image, this is one of a handful in Le Antichità Romane (including the previous image of the House of Cola di Rienzo) that, through their links to the lengthy Index to the “Pianta di Roma,” demonstrate his ambitious reinterpretation of the medium of the book as a sequential collection of interlinked images and texts. Piranesi’s presentation of information here uses visual composition, terminology, and book design in ways that remediate antiquity. The image contains four alphabetic markers, but its related text appears across two index entries, where he explains that A, B, C, and E (he skips D) identify features including evidence of missing decorations and the structure’s historical use as a tower.   

Piranesi depicts this arch in an earlier work, his Antichità Romane de’ tempi della repubblica of 1748 (below, left) and a later image from the Veduta di Roma series (below, right).  
Piranesi’s renderings of this structure in both of the other images, from roughly ten years earlier and later, demonstrate notable contrasts: the image from Antichità Romane (left) is the most authentic to the archway’s form, while both the earlier and later vedute expand the structure and exaggerate its proportions, suggesting the magnificence and solidity Piranesi favored in ancient Roman architecture.  
The captions from these three images of the same structure demonstrate Piranesi’s uniquely integrated presentation of information through verbal and visual media. Their text bears notable differences. The first (above left) emphatically declares the structure’s contemporary name and the artist’s ownership with “TEMPIO DI GIANO” [Temple of Janus] in the left slab and “PIRANESI FECIT” [Made by Piranesi] in the right slab. The caption in the image from Antichità Romane (above center) emphasizes the past, with “Vna delle due Fornici di Stertino” and its Latinate lettering (“Vna”) and terms (“Fornici”). The image from the Vedute di Roma (above right) calls attention to the structure’s contemporary designation by labelling it exclusively in Italian as “Tempio volgarmente detto di Giano.” Visually, the caption for the image from Le Antichità Romane stands out for its two prominent cracks against a clear background. If the use of trompe l’œil in antiquarian images tends to call attention to historical and contemporary media (Lolla), then this caption’s fissured stone, together with its antiquated language and the image’s informational structure, foregrounds Piranesi’s ambitious use of media—etching, print, and, importantly, the book. If the ideal of “the Enlightenment index” attempts to materialize universal knowledge (Pasanek and Wellmon), Piranesi pursues a similar ideal that in this case creates a material sense of distance. In this accurate image, the absence of annotation text—text that points, in some cases, to evidence of what is lost—amplifies the material absence and temporal distance that Piranesi highlights through his design of this volume and his visual composition in this image. (JB)