In 65-66 CE, the emperor Nero minted this copper as to emphasize his closing of the doors of the Temple of Janus to signify that Rome was at peace. This coin, one of nine issues (see this sestertius) with the inscription ARA PACIS, most likely refers to the great Altar of Augustan Peace on the northern Campus Martius decreed by the Senate in 13 BCE and dedicated on 30 January 9 BCE, where annual sacrifices to the allegorical goddess Pax were held thereafter. These coins (together with a similar coin issued by Domitian) testify to the continuing significance of this monument in Roman symbolism.
However, by the time of Domitian the level of the northern Campus Martius had risen to the level of the Via Flaminia due to various natural occurrences, including regular flooding of the Tiber, necessitating raising the travertine pavement of the Horologium Augusti, recalibrating the sundial, and burying the steps at the western entrance of the precinct. By the time of Hadrian the ground level had risen to the upper processional friezes on the the enclosure walls, and in 123 CE Hadrian enclosed the entire precinct with approximately 6-foot brick walls in an effort to protect it (see drawing). By the early third century CE the monument was almost completely buried.
It was not until the sixteenth century that some of the reliefs from the altar were discovered beneath the Palazzo Peretti (later the Palazzo Fiano-Almagia) on the modern Via del Corso in Rome, although these reliefs were not connected with the Ara Pacis when first discovered. The reliefs were scattered, some incorporated in the walls of the Villa Medici, some sent to the Uffizi Museum in Florence and to the Louvre in Paris. In 1859 repair work on the palazzo led to the discovery of the podium of the altar and more reliefs, and in 1879 these were finally recognized as belonging to the Ara Pacis. Many technical difficulties prevented complete excavation of the altar beneath the four-story palazzo, and it was not until 1937-38 that these problems were overcome by freezing the ground under the palazzo. The podium was thoroughly studied but left in place, but all the relief slabs were removed and the panels regained from the Uffizi (but not from the Louvre or Villa Medici--casts were made of these). The altar was reconstructed in a different location, near the Mausoleum of Augustus along the Tiber, and on 23 September 1938, the birthday of Augustus and final day of the Augustan bimillenary year, Mussolini inaugurated the restored altar, putting himself forward as the founder of the second empire of Rome. In 2005, the altar was housed in a new museum designed by the American architect Richard Meier.
Due to the long and complicated history of the altar's discovery and restoration, many questions and interpretative details are still being debated by modern scholars. The entire monument was originally constructed of white Luna marble, with all surfaces but the base covered with brightly painted reliefs. The precinct was mounted on a nearly square marble base measuring 11.630 meters (ca. 38 feet) on the eastern and western sides, and 10.625 meters (ca. 35 feet) on the north and south sides. Above the base the enclosure walls rose 6.3 meters high (ca. 21 feet). The coins of Nero suggest that doors enclosed the two entrances and that the cornice (now completely lost) was more elaborate, with fluted projections (acroteria) on the four corners. The presence of two entrances to the altar precinct was very unusual, perhaps suggested by the shrine of Janus in the Roman Forum, indicating passage from one state to another, such as peace and war.
The sacrificial altar inside the precinct sits on a podium with 4 steps, while the table for offerings is reached by 4 more steps; walls with relief decorations rise on three sides, two of which are crowned by slabs with beautifully carved vegetal volutes ending in winged lions. The internal altar is the most damaged part of the monument, since one of the foundations of the palazzo rested on its center, but its walls were also lavishly covered with reliefs, probably of female figures representing pacified provinces (such as this later relief from the Temple of Hadrian). Since the interior space around the altar is so cramped and since the enclosure walls would prevent spectators from seeing any sacrifices performed at the altar, scholars argue that the annual animal sacrifices must have been performed outside the precinct, though represented symbolically on the small friezes inside.
Scholars now agree that at least 2 of the slabs on the processional panels on the north and south enclosure walls were joined incorrectly during the 1937-38 reconstruction. All of the high-relief heads on the north wall are restorations, many of them complete recreations carved by the Italian sculptor Francesco Carradori in the late eighteenth century (compare this late-sixteenth-century drawing of one relief slab from the north wall and its restored appearance). The heads on the south wall were better preserved, but some have been added (e.g., the child Gnaeus Domitius Ahenobarbus) and noses and other body parts have been restored. Identifications of specific individuals are still hotly debated, except for Augustus, Agrippa, Antonia Minor, Drusus, their son Germanicus, and perhaps the Ahenobarbus family. The woman behind Agrippa is sometimes identified as Julia, daughter of Agustus, and some scholars still contend that the two boys in barbarian dress represent Gaius and Lucius Caesar. Perhaps exact identifications were not a necessary part of the sculptural program, so long as it was clear that members of the extended imperial family (the domus Augusta) were seen as essential to the peace that Augustus claimed as his achievement.
Of the panels on the east and west entrances, the Tellus/Pax panel is the best preserved, though even that now has extensive restorations. The fertility goddess with two infants (such as this figure from the bottom of the cuirass of the Prima Porta statue of Augustus) could have many symbolic associations simultaneously, but clearly the dominant message was one of natural abundance and peace. The Roma panel is very poorly preserved, but the concept of a helmeted goddess seated on armor and shields, symbolizing the military conquest on which Roman peace was founded) is well known from coins and other monuments, such as this relief from the Ara Gentis Augustae in Carthage, thought to be partly based on the Ara Pacis relief. On the western side, the Romulus and Remus panel is also very fragmentary, but the details of the scene can be reconstructed from coins such as this Republican denarius depicting the shepherd Faustulus and the she-wolf suckling the twins beneath the fig tree with a bird.
Sources:
Rehak, Paul. Ed. John G. Younger. Imperium and Cosmos: Augustus and the Northern Campus Martius. Madison: University of Wisconsin Press, 2007.
Rhyne, Charles and Reed College. Ara Pacis Augustae. URL: http://cdm.reed.edu/ara-pacis/.
Rossini, Orietta. Trans. Stephano Fox. Ara Pacis. Rome: Electa, 2007.