Flag of Russia (Eagle) - Русский орел флаг

The double-headed eagle is a common symbol in heraldry and vexillology. It is most commonly associated with the Byzantine Empire, the Holy Roman Empire, the Serbian Empire, the Russian Empire and their successor states. In Byzantine heraldry, the heads represent the Emperor having authority over both secular and religious matters, Byzantine emperors were regarded as Christ's viceregent on Earth. It also signified the dominance of the Byzantine Emperors over both East and West. In the Holy Roman Empire's heraldry, it represented the church and the state. Several Eastern European nations adopted it from the Byzantines and continue to use it as their national symbol to this day.