The Saturnalia were the most important religious feast in ancient Rome, celebrated in the days of the Winter Solstice (December 21), when the Sun seemed to struggle to rise again and the apparent death of Nature had to be exorcised with special rituals, so that the Sun would resume its course.
The Saturnalia were a rite of passage from the Old Year to the New Year, very similar to our Christmas and New Year's Eve celebrations. Gifts were exchanged, a banquet was prepared to cheer up the long night vigil, waiting for the Sun of the new year to rise. There was a game very similar to today's bingo: the numbers also had oracular functions, and were used to predict the future. Shops, schools and courts were closed, wars were suspended.
Originally, the Saturnalia were dedicated to the god Saturn, who was later superimposed by Dionysus, and with him, to the old rituals wild parties and abundant libations typical of his cult were added.
Sol Invictus was the invincible Sun, who was reborn every day and every year to a new life and defeated darkness and Death. The emperor Hadrian was depicted as Sol Invictus driving the Quadriga of the Sun in an enormous bronze sculpture that crowned his Mausoleum, today’s Castel Sant'Angelo in Rome, as we explain in the book «Castel Sant'Angelo. Mausoleum of Hadrian. Architecture & Light».
In the 3rd century AD, the Saturnalia merged with the cult of Sol Invictus, an oriental solar deity that had been imported by the emperor Elagabalus in 218 AD.
In 274 AD the emperor Aurelian made it the official state cult: the Sol Invictus was Dominus Populi romani, and the emperor became Dominus et Deus, deified already in life as a descendant of the Sun god by birth.
Many Roman buildings are oriented in such a way as to create illuminations only on the days of the Winter Solstice. They were a sacred luminous signal: those were the right days to celebrate rituals related to Saturnalia and Fors Fortuna, as we explain in detail in our book «Villa Adriana. Architettura Celeste. I Segreti dei Solstizi» which you can buy on this site (Itlian edition onnly).
We discovered it in Villa Adriana in Tivoli, in the buildings of Roccabruna and Accademia.
In the Accademia the Sun enters through a door and its rays illuminate the building along its entire length, even crossing the Temple of Apollo, on the days of the winter and summer Solstice.
In Roccabruna the same thing happened in the Tempietto on the upper floor (destroyed), where the Sun entered from the main door, located at the top of a flight of steps. The Tempietto must have resembled the one seen in a fresco of Herculaneum, preceded by a flight of steps. In the domed hall on the lower floor of Roccabruna a special light conduit still creates a Circle of Light on the days of the Winter Solstice, while on those of the Summer Solstice a Blade of Light can be seen.