Significance of sun alignment with two Roman monuments

Significance of sun alignment with two Roman monuments

An archaeo-informaticist from Indiana University has used virtual simulations to turn back the clock over two thousand years to show the significance of an alignment of the sun with two monuments tied to the founder of the Roman Empire – Caesar Augustus.

For half a century, scholars had associated the Ara Pacis, the “Altar of Peace” (dedicated in 9 BCE to Emperor Augustus), and the Obelisk of Montecitorio (a 71-foot-high granite monument brought by Augustus from Egypt), with the 23rd September – the founder’s birthday.

Research had previously shown that on this day, the shadow of the obelisk (which served as a gnomon, for a giant sundial on the plaza floor), would point toward the middle of the Ara Pacis. The Senate had commissioned the Ara Pacis to recognise the peace brought to the Roman Empire through Augustus’ military victories.

Another explanation

However, informatics and computing professor Bernie Frischer announced that there was another explanation for the original placement of the two landmarks that lay both parallel and adjacent to a major road, the Via Flaminia. This road led from Rome over the Apennine Mountains to the coast of the Adriatic Sea.
“What’s important is not the shadow of the obelisk, but the sun’s disk seen over the centre of the top of the obelisk from a position on the Via Flaminia in front of the Ara Pacis,” Frischer said. New computer simulations now show that German scholar Edmund Buchner’s long-standing theory that the shadow of the obelisk hit the centre of the façade of the Ara Pacis was wrong.

Campus Martius

GPS coordinates, known dimensions and additional bibliographical sources were also used to create the 3-D 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 said his Rome-based 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 a team that included John Fillwalk, director of the Institute for Digital Intermedia Arts at Ball State University, determined that the Sun’s placement at the top of the obelisk occurred on the 9th October.
“Inscriptions on the obelisk show that Augustus explicitly dedicated the obelisk to his favourite deity, Apollo, the Sun god,” Frischer said. “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. The new date of the alignment, the 9th October, is actually what we know to be the annual festival of the Temple of Palatine Apollo.

Using virtual environments

The work is a statement to the possibilities inherent in using information technology to support the work of archaeologists, and specifically for Frischer, the use of 3-D modelling.
“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 said. “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.”

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