into the Western (Catholic) and Eastern (Orthodox) churches. In 1448, not long before the Byzantine Empire collapsed, the Russian Orthodox Church gained independence from the Patriarch of Constantinople. As a result of the redevelopment of Western Europe, and the gradual fall of the Eastern Roman Empire to the Arabs and Turks (helped by warfare against Eastern Christians), the final Fall of Constantinople in 1453 resulted in Eastern scholars fleeing the Muslim hordes bringing ancient manuscripts to the West, which was a factor in the beginning of the period of the Western Renaissance there. Rome was seen by the Western Church as Christianity's heartland. Some Eastern churches even broke with Eastern Orthodoxy and entered into communion with Rome (the "Uniate" Eastern Catholic Churches). Protestant Reformation The changes brought on by the Renaissance eventually led to the Protestant Reformation during which the Protestant Lutheran and the Reformed followers of Calvin, Hus, Zwingli, Melancthon, Knox, and others split from the Catholic Church. At this time, a series of non-theological disputes also led to the English Reformation which led to the independence of the Church of England. Then, during the Age of Exploration and the Age of Imperialism, Western Europe spread the Catholic Church and the Protestant churches around the world, especially in the Americas. These developments in turn have led to Christianity being the largest religion in the world today. Catholic tradition The Catholic Church teaches in its doctrine that it is the original church founded by Christ on the Apostles in the 1st century AD. The papal encyclical Mystici corporis (Pope Pius XII, 1943), expresses the dogmatic ecclesiology of the Catholic Church thus: "If we would define and describe this true Church of Jesus Christ—which is the One, Holy, Catholic, Apostolic, Roman Church–we shall find no expression more noble, more sublime, or more divine, than the phrase which calls it 'the Mystical Body of Jesus Christ'." The Second Vatican Council's dogmatic constitution, Lumen gentium (1964), further declares that "the one Church of Christ which in the Creed is professed as one, holy, catholic and apostolic, ... constituted and organized in the world as a society, subsists in the Catholic Church, which is governed by the successor of Peter and by the Bishops in communion with him". Likewise, the encyclical of Pope Pius IX, Singulari Quidem, states in a similar vein, "There is only one true, holy, Catholic Church, which is the Apostolic