Scientists have used latest technology to produce virtual simulations of an Egyptian obelisk and the famous Ara Pacis (Altar of Peace) in ancient Rome to solve a mystery surrounding the ancient obelisk , which functions as a giant sundial. The 3D reconstruction they produced shows how the sun would have lined up with the obelisk and the altar.

The Ara Pacis, or "Altar of Peace," is an altar in Rome dedicated to Peace, the Roman goddess, and commissioned in 13 BC to honour the return of Augustus to Rome after his three years in Hispania and Gaul. Today the building is recognized as a masterpiece of Augustan architecture, and it is housed in a glass, cube-shaped museum along the Tiber River. But in ancient times, it would have stood in the northern outskirts of the city, near an Egyptian obelisk that the Romans took from Heliopolis and repurposed as a gnomon, or giant sundial.

Obelisks were built as early as 3500 B.C. Their moving shadows enabled the partitioning of the day into two parts by indicating noon. They also showed the year's longest and shortest days when the shadow at noon was the shortest or longest of the year. Later, markers added around the base of the monument would indicate further time subdivisions.

It was believed, according to a theory put forward by German scholar Edmund Buchner, that the shadow of the obelisk would hit the centre of the facade of the Ara Pacis on Augustus' birthday, 23 rd September.

However, Bernard Frischer, a professor of informatics and computing at Indiana University Bloomington, put together a 3D simulation of the Ara Pacis in its original context, to demonstrate a technical point related to publishing interactive simulations on a webpage, and was surprised to discover that Buchner’s theory was wrong. According to the simulation, the sun would have appeared on top of the obelisk not on Augustus’ birthday, but on 9 th October, the annual festival of the Temple of Palatine Apollo.

The Temple of Palatine Apollo was the most lavish new temple that Augustus built, and inscriptions also show that Augustus dedicated the obelisk to Apollo. So while Buchner’s theory was disproved, it nevertheless revealed Augustus’ dedication to his favourite deity and patron god.

By April Holloway