The Orthodox Church, commonly known internationally as the Orthodox Church or the Eastern Orthodox Church, is officially known as the Orthodox Church (Greek: Ορθόδοξη Καθολική Εκκλησία， Russian: Православная Католическая Церковь， Orthodox Catholic Church, together with Catholicism and Protestantism, is one of the three major schools of Christianity. It is based on orthodox theology and emphasizes the orthodoxy of the Apostolic Church. [1-2]
Eastern Orthodoxy originated from the belief in the savior of Greek civilization and is famous for the national religions of the Byzantine Empire and the Russian Empire, which were inherited in the eastern part of the Roman Empire. [3]
In the 1st century AD, the prototype of the Five Cities Federation of Greek Christians, including Jerusalem, Antioch, Constantinople, Alexandria, and Rome, was born. [4]
In the 4th century, Constantinople became the capital of the Roman Empire's national church. [4]
In the 11th century, there was a great split between the Eastern and Western churches, forming the Eastern Roman Orthodox Church. [5]
In the 15th century, the Eastern Roman Empire was defeated by the Battle of Constantinople. The establishment of the Eastern Orthodox Church system led by the Greek Orthodox Church and the Russian Orthodox Church. [5]
As of 2014, there were nearly 400 million Orthodox Christians worldwide, including 250 million followers of different denominations who were integrated with the Universal Patriarch. [6]
The Eastern Orthodox Church of the former Soviet Union was mostly governed by the Moscow Patriarch of the Russian Orthodox Church, with 160 million followers, making it the second largest single political and cultural group of Christians after the Vatican.

Orthodox religion
Eastern Orthodoxy, originally the orthodox branch of Christianity, refers to the geographical direction of the birth of Christian faith and the Eastern Christian and church system represented by Eastern Orthodoxy. [9]
Orthodoxy in English Writing[ ˈɔːθə D ɒ "Ks", derived from Greek“ Ορθόδοξος (orth ó doksos), by‘ ρθός’ (Continued) and“ δόξα” (Concept) consists of two parts. [10]
In the issue of the succession of the early church and apostles, it refers to "sufficient", "complete", and "without omission". Belonging to an ideology that has always existed in Christianity. [10]
The entity of the Eastern Orthodox Church is commonly known as the Orthodox Church (Eastern Orthodox Church), and its full name is the Orthodox Catholic Church.
Symbolizing the Christian Church and overall style of the 1st to 11th centuries, it integrates the five primitive autonomous churches of Jerusalem, Antioch, Alexandria, Byzantium (Constantinople), and Rome.
With the legalization and nationalization of Christianity in the Roman Empire, Constantinople became the "New Roman" capital church of the empire's political and religious unity, as well as the capital church of the entire Christianity. After the decline and disintegration of the Roman Empire, the concept of an independent church formed by independent regimes was born.