"The tips of the two phalli point to southeast, where the sun raises in the winter months," she said.
In the analysis that followed, Magli examined the original urban plan taking into account the complex natural horizon of the Alps in which Aosta's valley is nested.
The results confirmed Aosta's orientation to the sun rising on the winter solstice.
"We can estimate that the foundation of Aosta began on Dec. 23. On that day, the sun raises right in the direction pointed by the phalli on the stone," Bertarione said.
At those times, the winter solstice was indeed hosted by the sign of Capricorn. Although Augustus' astrological sign was the Libra -- he was born on Sept. 23 -- he chose the Capricorn as his emblem, possibly because it was the sign of his conception.
"Capricorn clearly fitted much better than Libra with the idea of renewal, traditionally associated with the midwinter sun," Magli said. "It was thus chosen to signify the new golden era of peace and prosperity."
"In this view, Aosta would have been built to reflect Augustus' associations with the 'cosmic' signs of renewal: the winter solstice and the Capricorn," he added.