The Byzantine Empire, also known as the Eastern Roman Empire, was a predominantly Christian state that promoted and upheld Christianity as its official religion. The empire emerged as the continuation of the Roman Empire in the East after the fall of the Western Roman Empire in 476 CE. The Byzantine Empire lasted for over a thousand years, from 330 CE to 1453 CE, and during this time, it played a crucial role in the preservation and spread of Christianity.

Christianity as the Official Religion:
- The Byzantine Empire was founded by Emperor Constantine the Great, who played a significant role in the Christianization of the Roman Empire. Constantine embraced Christianity and issued the Edict of Milan in 313 CE, which granted religious freedom to Christians and ended the persecution of Christians in the Roman Empire.
- Under Emperor Theodosius I, Christianity became the official state religion of the Roman Empire in 380 CE. This decision carried over to the Byzantine Empire, and Christianity remained the state religion throughout its existence.

Byzantine Christianity:
- The Byzantine Empire followed the Orthodox form of Christianity, which was distinct from Roman Catholicism in the West. The Byzantine Church, known as the Eastern Orthodox Church, had its own hierarchy and theological traditions.
- Byzantine Christianity was characterized by its rich liturgical practices, elaborate church architecture, and the veneration of icons. Iconography played a significant role in Byzantine religious life, and icons were seen as windows to the divine, promoting a deep sense of spirituality.

Role of the Church:
- The Byzantine Empire was closely tied to the Church, and the emperor held a unique position as both the political and religious leader of the state. The emperor was seen as the representative of God on Earth and the protector of the Orthodox faith.
- The Church played a vital role in the administration of the empire, as bishops and priests were responsible for overseeing local affairs and maintaining social order.

Legacy and Influence:
- The Byzantine Empire's promotion of Christianity had a lasting impact on the development of Eastern Europe and the Balkans. It served as a cultural and religious bridge between the Roman Empire and the medieval Christian kingdoms that emerged in Europe.
- Byzantine missionaries and scholars spread Orthodox Christianity to neighboring regions, including Russia, Bulgaria, and Serbia. The Byzantine Empire's influence can still be seen in the dominant presence of Eastern Orthodox Christianity in these areas today.

In conclusion, the Byzantine Empire promoted Christianity as its official religion, and its commitment to the Orthodox form of Christianity played a significant role in shaping its culture, politics, and influence across the Eastern Mediterranean and beyond.