Some buildings are astronomically oriented so that the Sun entered them ONLY in those days - creating special illuminations - which served to check the accuracy of the Calendar.

The Summer Solstice (June 21) and the Winter Solstice (December 21) are the most important dates for Archaeoastronomy, because in those days the Sun reaches the extreme points of its apparent path.
The buildings were astronomically oriented so that the Sun entered them ONLY on those days - creating particular illuminations - and thus the accuracy of the Calendar could be verified.

The Pontifex Maximus was the highest Roman priestly office: he controlled Time and therefore Power, because he established the duration of public and religious offices and the dates of sacred rituals, which had to take place on the right day to be pleasing to the divinities.

The Roman emperor as Pontifex Maximus was the semi-divine intermediary between men and gods. The emperor could boast that he was so powerful that he even commanded the course of the sun. For this reason, special illuminations take place on the days of both the summer and winter Solstices.

The Sun has always been a sacred symbol of Divinity. Light versus Darkness, or Life on one side and Death on the other: the ancestral fears of man. Since the time of the Pharaohs the sovereign was identified with the Sun; the Hellenistic dynasts were divine. Roman emperors became divine after their death. In any case power was given to emperors by the gods.

We discovered illuminations at the Summer Solstice in several ancient Roman buildings.

First of all at VILLA ADRIANA, where at sunset the Sun still floods the Academy and the Temple of Apollo with light for its entire length. In Roccabruna the Sun creates a Blade of Light inside the large domed hall.

‼️ Blade of Light video on my Youtube channel: https://www.youtube.com/watch?v=DWCrdMaUG6o

We discovered them in the MAUSOLEUM OF HADRIAN (Castel Sant'Angelo), where the Sun creates a rectangle of light in the Sala delle Urne (the burial chamber), at 9 am and 4 pm, inside the niches where the sarcophagi once stood. Divine signs linked to the immortality of the emperor and of the members of his family, who were all deified after death.

We discovered them in SPERLONGA, where the setting sun enters the large Grotto of the Villa of Tiberius and illuminated the statues of Ulysses blinding Polyphemus. It alludes to the semi-divine descent of Tiberius and the Gens Claudia from Telegono (son of Ulysses and the sorceress Circe), and legitimizes their succession.

We also discovered them in SPLIT (Croatia) in Diocletian's Palace thanks to Zlatko Andrijasevic, where the Sun illuminates the north door of the Vestibule towards the great Peristyle and probably illuminated sculptures placed in its niches.

They are visible also in the PANTHEON where  from June 7th to July 7th a hue circle of light illuminates the center of the pavement.