Event
Date: 2026/09/04
PANTHEON: THE ARC AND THE SQUARE OF LIGHT IN SEPTEMBER
Once again this year – as always on September 4, 5 and 6th – the spectacular September illuminations were visible: the Arc of Light and the Square of Light.
The Arc of Light perfectly matches the masonry arch visible above the entrance portal; the light precisely matches the arch's horseshoe shape.
This illumination is the result of incredibly precise calculations: the dome's oculus — through which the Sun's rays enter — has a diameter of nine meters, matching the nine-meter width of the masonry arch above the portal.
The Square of Light illuminates a marble square, set into the floor in front of the portal itself, a square that encloses a circle.
This occurs because the top of the portal cuts across the circle of light, aligning it with the floor's square, which has the same width as the portal.
These luminous "special effects" were designed and created 1,900 years ago by one of ancient Rome's greatest architects, Apollodorus of Damascus, who certainly possessed neither computers nor artificial intelligence.
Those sacred illuminations (hierophanies) had a specific symbolic meaning linked to the cults of differen deities; the square containing a circle was also a sacred symbol.
We explain this in detail—along with the building techniques and other marvels of this extraordinary building in the book «Pantheon. Architecture and Light», also in English edition, published by Rirella Editrice.