Octavian, Augustus Caesar, had a private cult of Apollo, which meant a few privileged persons could have in their possession a piece of jewelry like this, no doubt a mark of prestige, showing a certain level of trust, for the emperor was not deified until after his death, and so wouldn’t be fit for public display featuring as the Sun God.
The Greek idea of allegory referred to a public domain; in the agora the rhetorical apparatus was deployed to address a quality difficult to discern by gazing directly at the physical person; and so, in plastic arts allegory became an extension of simile, where the use of “like” would seem very appropriate.
In the Middle Ages the scholastic grab bag allowed an indiscriminate use of logical and rhetorical; for example, the Catholic church could be treated as body with its own head, and Jesus was the King of Heaven. Without this new dimension in allegorical thinking, its inclusion in the Medieval bestiary, where the state is often represented as animal, the later statement of Louis XIV, I am the state wouldn’t be possible.
The modernity chose not to confront the language of religion but to further inflate it: this is why there were personifications of genres of poetry, seasons, hours of the day and the continents. We could say that the XVII century allegory competed with religion, while the XVIII century allegory effectively replaced it.