Astronomical orientation and light phenomena in Roccabruna

During the first International Meeting “Rileggere l’Antico”, held in Rome in december 2004, Roccabruna was considered an astronomical Observatory and there was a presentation about a supposed armilla hanging inside its inner dome1.

Fig. 29 - Reconstruction of the armilla suspended inside the dome of hall RB6 (from Cinque-Lazzeri 2010)

After observing the light phenomena in the Temple of Apollo in the Accademia, I noticed that the Accademia Esplanade and Roccabruna had exactly the same orientation (see plan figure 4), therefore I started thinking about a possible orientation of Roccabruna.

The starting point was an article by professor Vittorio Castellani, who rejected the hypothesis that the building had been oriented towards the sunset of august 11th, which was the day when Hadrian became emperor, the Dies Imperii. He wrote2:

“The direction towards which Roccabruna is oriented finds no explanation in the topography of the site, and maybe supports the hypothesis of an orientation toward the sunset on Summer solstice”. Finally he decided that this last is “perhaps the only acceptable hypothesis”3, without further developing the idea.

During the 8th Conference on Archaeoastronomy Mensura Caeli, held in Ferrara (Italy) in 2008, Giuseppina Cinque ed Elisabetta Lazzeri proposed that the conduits passing through the dome of Roccabruna were housing large beams, which supported a gigantic armilla suspended under the ceiling. There also was a very unlikely reconstruction of the center of the pavement, with an image of an armilla copied from a mosaic at Solunto (figure 29). They wrote4:
“The analysis based on such data made us rule out all hypothesis according to which the conduits were made to obtain particular and evocative illuminations inside the central hall. This idea is absolutely impossible, since the position of the two conduits on the south-eastern side forbids any kind of illumination by the Sun. ... The only possible solution is to consider the conduits as housing for beams which were sustaining some heavy ornamental object which was suspended under the center of the dome.”

The armilla theory cannot be accepted for a series of reasons:

Which was the function of these conduits, then? For one of them, the solution was given to me by the american architects Robert Mangurian and Mary-Ann Ray, who between 1985 an 1994 surveyed the whole Villa Adriana with their Atelier Italia project.

After working at the project of the Clos Pegas Winery in Napa Valley, (California, USA), which had an equinoctial alignment, they asked themselves if the radial orientation of the buildings of Villa Adriana could be due to astronomical orientations.

Fig. 30-31 - Roccabruna, june 19th, 2009. Left: the Sun illuminating the apsed niche in front of the entrance; the light beam shines on the dome below the inner slot of conduits D-E. Right: the Sun enters from the main door and from the inner slot of conduit B (photo Marina De Franceschini)

On june 21st, 1988, the day of Summer solstice, they went to Roccabruna at sunset, and discovered the extraordinary light phenomena which occur there5.

At sunset, in fact, the Sun enters through the main door illuminating the niche on the opposite side, something that happens during most of the summer days. But only in the days of the Summer Solstice the Sun penetrates also into the conduit located above that door: its rays come out from the slot inside the dome projecting a rectangular light blade on the opposite side. This blade slowly moves with an arched course, until when the Sun sets and ‘switches off’.

On june 13th, 2009, a week before the Solstice, I verified that the Sun shines through the main door, illuminating the niche on the opposite side, but there was no light blade.

Roccabruna - Summer Solstice 2009 and 2011

On june 19th, 2009, instead, I observed the phenomenon described by Robert and Mary-Ann: the Sun penetrated in the conduit, and the light came out from the inner slot, projecting a light blade on the opposite side of the dome (figures 30 and 31). The light blade slowly moved from left to right with an arched course, on top of which it coincided with the slot where conduits D-E open inside the dome (figure 32).

The same light phenomena happened also in the temple that once existed on the upper floor of Roccabruna, which was oriented along the same axis connecting the dawn of Winter Solstice to the sunset of Summer Solstice (figure 33).

During Winter Solstice, the Sun was rising at the center of the main door of the temple, while during Summer Solstice it was setting through the window on the opposite side.

We also plan to study other light phenomena which were created by the central oculus of the dome that covered the temple.

Fig. 32 - Photo sequence of the light phenomena at Roccabruna. The light blade is moving from left to right and goes down, becoming red. The pictures were taken on june 19th, 2009 (photo Marina De Franceschini)
Fig. 33 - Plan of the Temple of the upper floor of Roccabruna with its orientation towards the Solstices (elaboration from Lugli 1940)

From these discoveries and our study, it is clear that Accademia and Roccabruna have been planned with an astronomical orientation exactly as the Horologium Augusti, the Domus Aurea and the Pantheon in Rome.

During the Solstices there were light phenomena signaling a particular moment during the year. Winter Solstice, in fact, meant the apparent death of Nature, while Summer Solstice coincided with the ripest period of harvest and flowering.

Since the times of Augustus, buildings planned as ‘solar machines’ were part of the iconography of the imperial power, since the emperor - as Pontifex Maximus - superintended to the Calendar and therefore to the rites and ceremonies linked to the cycle of the Time and the Seasons.

As we said, this booklet is anticipating the first results of our surveys and studies at Villa Adriana, which will be explained and fully discussed - also in their symbolic meaning - in a forthcoming book.


1 There is just an abstract of this presentation, the Proceedings have never been published
2 Castellani 2006, p. 18.
3 Castellani 2006, p. 11-13 with astronomical calculations based on an old measurement given by Maiuri in the 1930‘s.
4 Cinque-Lazzeri 2010, p. 119.
5 This discovery was briefly described in Mangurian-Ray 2008.