The theological debates for the orthodox doctrine
  As Christian intellectuals sought to establish a doctrine for the new religion, their varying interpretations gave rise to ardent theological debates. These were often fuelled by more earthly considerations, such as the control of large communities of worshippers and ecclesiastical estate, or the hierarchy between the patriarchal seats of Rome, Constantinople, Alexandria, Antioch and Jerusalem. Theological debates occasionaly acquired political significance, because of their large following in certain provinces: Arianism was widely spread in the barbaric Christian west, while Monophysitism, found its main support in the Syriac- and Coptic-speaking east.
  In an attempt to maintain the unity of the Church and its close relation to the State, the Early Byzantine emperors conveyed a series of ecumenical councils, which sought to define a single orthodox faith. The first Ecumenical Council, held in Nicaea (325), condemned Arianism, a theory which argued against the divine nature of Christ, and established his dual (both human and divine) nature. The second Council, held in Constantinople (381), introduced the concept of the Trinity - Father, Son and Holy Spirit - three aspects of a single divinity. The third Council (Ephesus, 431) condemned Nestorianism, and acknowledged the Virgin Mary as Mother of God. (Nestorianism held the Virgin Mary as being simply the Mother of Christ, because of her son's human nature.) The fourth Council, held at Chalcedon (451), defined the single nature of Christ as embracing both the human and the divine, indivisibly but without confusion. It condemned Monophysitism, according to which Christ had a single divine nature. A fifth ecumenical council, conveyed by Justinian (Constantinople, 553), sought, unsuccessfully, to reconcile the orthodox and the Monophysites.