In Rome, the symbol of Rome – the eagle – was often shown accompanied by a serpent. They symbolized good in the form of an eagle triumphing over evil, which was represented by a snake.
The origin of the eagle as a symbol dates back to the times of the Proto-Indo-European community when the eagle as a symbol of strength became an attribute of the first of the gods of the Proto-Indo-European pantheon – Diaus, known from later Greece as Zeus, and from Rome as Jupiter, Iuppiter (archaically Diouis pater). The eagle remained an attribute and messenger of Jupiter in Roman religion. As a symbol of the strength of this god, it became the emblem of the Roman legions, the likeness (figure) of an eagle with spread wings was on top of the banner of each legion.
In the Roman Empire, the eagle over time became the emblem of the emperor as the head of the army, and then the universal symbol of the Roman state. After the transfer of the capital to Constantinople and the consolidation of the dualistic character of the empire (divided into the Latin west and the Greek east), the symbolism of the double-headed eagle became widespread, where the two heads symbolize the two capitals: Rome on the west, Constantinople on the east.