Play Video

3D models find real reason for Rome’s ‘Altar of Peace’

This virtual simulation image shows the sun atop the obelisk with the Altar of Peace in the foreground. (Credit: Indiana U.)

Virtual simulations challenge the usual theory about why and when the sun aligns with the ancient Roman ‘Altar of Peace’ and a giant obelisk.

For nearly a half-century, scholars had associated the relationship between the Ara Pacis, the “Altar of Peace” dedicated in 9 BC to then-emperor Augustus, and the Obelisk of Montecitorio—a 71-foot-high granite obelisk Augustus brought to Rome from Egypt—with Augustus’ September 23 birthday.


Prevailing research had found that on this day, the shadow of the obelisk—serving as the pointer, or gnomon, of a giant sundial on the plaza floor—would point toward the middle of the Ara Pacis, which the Roman Senate had commissioned to recognize the peace brought to the Roman Empire through Augustus’ military victories.

Over his nearly 40 years of teaching Roman topography classes, Indiana University Bloomington School of Informatics and Computing professor Bernie Frischer had always informed students of that prevailing theory.

Recently, however, in an announcement made at the Vatican’s Pontifical Archaeological Academy in Rome, Frischer provided another explanation for the original placement of the two landmarks that were both parallel and adjacent to what was at the time the major road, the Via Flaminia, leading from Rome over the Apennine Mountains to the coast of the Adriatic Sea.

Virtual view of Augustus' Altar of Peace and the Obelisk of Montecitorio, background, as seen from the Via Flaminia, the ancient road from Rome to the Adriatic Sea. (Credit: Indiana U.)
Virtual view of Augustus’ Altar of Peace and the Obelisk of Montecitorio, background, as seen from the Via Flaminia, the ancient road from Rome to the Adriatic Sea. (Credit: Indiana U.)

Disproving the theory

“What’s important is not the shadow of the obelisk, but the sun’s disk seen over the center of the top of the obelisk from a position on the Via Flaminia in front of the Ara Pacis,” Frischer says.

New computer simulations now show that German scholar Edmund Buchner’s longstanding theory that the shadow of the obelisk hit the center of the facade of the Ara Pacis was wrong.

GPS coordinates, known dimensions, and additional bibliographical sources were also used to create the 3D models of the Ara Pacis, the meridian, and the obelisk, all of which would have been located at the 490-acre site then known as the Campus Martius.

Frischer says his Rome-based research assistant Ismini Miliaresis conducted critical research on the meridian line location, and independent scholar and professional meridian designer and engineer Paolo Albèri Auber conducted the refined work on the obelisk’s original size.

Using NASA’s Horizons System, which gives the position of objects in the solar system in the sky at any time in history as seen from any spot on earth, along with surveys of the location of the sundial’s original meridian line, and the height of the obelisk in exacting detail, Frischer and colleagues determined the sun’s placement at the top of the obelisk occurred on October 9.

Happy birthday, Apollo

“Inscriptions on the obelisk show that Augustus explicitly dedicated the obelisk to his favorite deity, Apollo, the Sun god,” Frischer says. “And the most lavish new temple Augustus built, the Temple of Palatine Apollo, was dedicated to his patron god and built right next to Augustus’ own home.

“So the new date of the alignment, October 9, is actually what we know to be the annual birthday festival of the Temple of Palatine Apollo,” he says. “No other date on the Roman religious calendar would have been as appropriate as this.”

While team member John Fillwalk and the Institute for Digital Intermedia Arts Lab at Ball State created one interactive model that runs in the game engine Unity, Indiana University School of Informatics research scientist Matthew Brennan used AutoCad and 3D Studio Max to create a photorealistic model the team used to generate images and video clips illustrative of the research.

Frischer then sought independent confirmation of the findings from Lawrence Livermore National Laboratory astrophysicist David Dearborn.

“He ran independent tests of our solar alignments, using different software and methods, and his conclusions confirmed what we had found, giving us added confidence that our discovery is correct,” Frischer says.

Bringing the past back

“Empiricism, that sense of direct observation of nature through the senses, in some cases has had to give way to thought experiments and likewise, to computer simulations, as objects of study recede beyond our innate sensory apparatus in time, space, and scale,” he says.

“I call it ‘simpiricism,’ where we create computer simulations to bring our object back within the ken of the natural senses so it can be observed again, in a way analogous to what was done in the time of classic empiricism.”

“3D modeling can show scholars and, indeed, the general public, what the archaeologist uncovered, and it can be used to provide a view of how the site or object looked when it was new and in subsequent stages of its use and destruction,” Frischer says.

The National Science Foundation funded the research.

Source: Indiana University