 Complete the following phrase:  Earlier in the 4th century, following the Diocletianic Persecution of 303313 and the Donatist controversy that arose in consequence, Constantine the Great had convened councils of bishops to define the orthodoxy of the Christian faith and to expand on earlier Christian councils. A series of ecumenical councils convened by successive Roman emperors met during the 4th and the 5th centuries, but Christianity continued to suffer rifts and schisms surrounding the theological and christological doctrines of Arianism, Nestorianism, and Miaphysitism. In the 5th century, the Western Roman Empire decayed as a polity; invaders sacked Rome in 