page_title: State church of the Roman Empire
section_title: Rise of Islam
hierarchical_section_title: State church of the Roman Empire / History / Rise of Islam
caption_attribution_description: Age of the Caliphs
context_page_description: With the Edict of Thessalonica in 380 AD, Emperor Theodosius I made Nicene Christianity the Empire's state religion. The Eastern Orthodox Church, Oriental Orthodoxy, and the Catholic Church each claim to stand in continuity with the church to which Theodosius granted recognition, but do not look on it as a creation of the Roman Empire.
  Earlier in the 4th century, following the Diocletianic Persecution of 303–313 and the Donatist controversy that arose in consequence, Constantine had convened councils of bishops to define the orthodoxy of the Christian faith, expanding on earlier Christian councils. A series of ecumenical councils convened by successive emperors met during the 4th and 5th centuries, but Christianity continued to suffer rifts and schisms surrounding the issues of Arianism, Nestorianism, and Miaphysitism. In the 5th century, the Western Empire decayed as a polity: invaders sacked Rome in 410 and in 455, and Odoacer, an Arian barbarian warlord, forced Romulus Augustus, the last nominal Western Emperor, to abdicate in 476.
context_section_description: The Rashidun conquests began to expand the sway of Islam beyond Arabia in the 7th century, first clashing with the Roman Empire in 634.
  That empire and the Sassanid Persian Empire were at that time crippled by decades of war between them.
  By the late 8th century the Umayyad caliphate had conquered all of Persia and much of the Byzantine territory including Egypt, Palestine, and Syria.
  Suddenly much of the Christian world was under Muslim rule. Over the coming centuries the successive Muslim states became some of the most powerful in the Mediterranean world.
  Though the Byzantine church claimed religious authority over Christians in Egypt and the Levant, in reality the majority of Christians in these regions were by then miaphysites and members of other sects. The new Muslim rulers, in contrast, offered religious tolerance to Christians of all sects. Additionally subjects of the Muslim Empire could be accepted as Muslims simply by declaring a belief in a single deity and reverence for Muhammad (see shahada). As a result, the peoples of Egypt, Palestine and Syria largely accepted their new rulers and many declared themselves Muslims within a few generations. Muslim incursions later found success in parts of Europe, particularly Spain (see Al-Andalus).
caption: A map of Muslim expansion in the 7th and 8th centuries.
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