HADRIAN'S VILLA IN TIVOLI: ROCCABRUNA AND ITS LIGHT
Today, only the lower floor of Roccabruna remains, a large quadrangular masonry cube; but it originally had an upper floor with a small Temple, which could be seen from the surrounding countryside and signaled the emperor's presence to everybody (today, its architectural marble fragments are left, scattered across the grounds).
Visitors to Hadrian's Villa don't always reach this mysterious building, following a path that passes through an ancient olive grove and starts from the Antiquarium.
It's worth the effort, because today in place of the small Temple, there is a panoramic terrace with a view that sweeps all around, all the way to Rome.
On clear days, even see the dome of St. Peter’s can be seen, and this means that, in Roman times, Hadrian's Mausoleum (Castel Sant’Angelo), was visible.
On the lower floor of Roccabruna there is a large circular Hall covered by a blind dome, which has three-meter-thick perimeter walls. The Temple on the upper level also had a dome, and an octagonal cella surrounded by sixteen Ionic columns: it rested on the perimeter walls so as not to weigh down on the dome of the lower floor. Thus, Roccabruna had two superimposed domes, one on top of the other, a true architectural feat.
The lesser-known features of the Roccabruna building are described in detail in our book «Villa Adriana. Architettura Celeste. I segreti dei Solstizi» (Italian edition only) published by Rirella Editrice.
For example, it describes the walls of the large circular Hall, which had a diameter of nine meters, whose walls were revetted with in precious marble. Also the floor was made of marble, an opus sectile with rows of concentric triangles, of which only the imprints remain. The dome was plastered; some scholars believe it was covered in mosaics decorated with stars, but nothing remains, only some blue tesserae which are in the storerooms.
At the center of the lower floor, above the main door, there is a rectangular opening that is repeated identically on the other two façades: three masonry conduits, cut into the thickness of the walls, which emerge with three slits inside the dome of the circular hall.
The three conduits had a very specific function, which we discovered thanks to archaeoastronomy and the astronomical calculations of Giuseppe Veneziano. They served to create extraordinary illuminations (hierophanies) visible only in the days of the Summer Solstice (June 21) and the Winter Solstice (December 21). Other hierophanies occurred in the Temple on the upper floor on those same dates.
At sunset on the Summer Solstice, the Sun's rays still enter inside the light conduit above the entrance door, creating a Blade of Light inside the dome; It lasts for over an hour, it moves along an arc, it turns red, and then goes out, as seen in the video.
👉 See the Blade of Light in this video:
At that same moment, the Sun sets in the center of the main door of the circular Hall and illuminates the niche on the opposite side, where probably was a statue of the goddess Isis; a candelabra base with the goddess's symbols, including a sistrum, a torch, and asps, was found in the building.
During the Summer Solstice, the Romans celebrated the feast of Fors Fortuna, an ancient local deity, associated with the Egyptian goddess Isis. The same cult existed in the Temple of Fortuna Primigenia in Palestrina, which is dedicated to the goddess Isis-Fortuna and, on clear days, is visible from the panoramic terrace of Roccabruna.
The symbolic meaning of the illuminations at Roccabruna, and of others that occurred in the Accademia building on the days of the two Solstices, is explained in detail in our book «Villa Adriana. Architettura Celeste. I segreti dei Solstizi».
Both buildings stood on the Accademia Esplanade, which was the true Acropolis of the Villa, closer to the divinity, inserted into a Sacred Landscape.
Roccabruna, as mentioned, was dedicated to the goddess Isis, while the Accademia was dedicated to Osiris-Dionysus, as proved by the discovery of the statues of the Old Centaur and the Young Centaur, which were part of the Dionysian procession.