"Although Christian "clergy," such as bishops and deacons, begin to appear around the year A.D. 100 in early Christian communities, priests emerge as Christian leaders only much later. Priests came to be the ordained clergy tasked with officiating rituals like the Eucharist or Lord's Supper, also known as Communion. And what about their celibacy? Even here, evidence is both unclear and late: there were reports that some bishops at the Council of Nicea, called by Emperor Constantine in A.D. 325 to address the problem of heresies, argued for a consistent practice of priestly celibacy. This, however, was voted down at the conclusion of the council. The debate resurfaced a couple of hundred years later, but still without uniform agreement. Over time, priestly celibacy became a serious point of disagreement between the Eastern Orthodox and the Western Roman Catholic churches and contributed to the Great Schism between the two in A.D. 1054. Pope Gregory VII attempted to mandate priestly celibacy, but the practice was contested widely by Christians in the Orthodox Eastern Mediterranean world. Five centuries later, the issue was once again at the forefront of debate when it became a significant factor in the Protestant split from Catholicism during the Reformation."