"The Council of Nicaea, the first ecumenical debate held by the early Christian church, concludes with the establishment of the doctrine of the Holy Trinity. Convened by Roman Emperor Constantine I in May, the council also deemed the Arian belief of Christ as inferior to God as heretical, thus resolving an early church crisis.
The controversy began when Arius, an Alexandrian priest, questioned the full divinity of Christ because, unlike God, Christ was born and had a beginning. What began as an academic theological debate spread to Christian congregations throughout the empire, threatening a schism in the early Christian church. Roman Emperor Constantine I, who converted to Christianity in 312, called bishops from all over his empire to resolve the crisis and urged the adoption of a new creed that would resolve the ambiguities between Christ and God.
Meeting at Nicaea in present-day Turkey, the council established the equality of the Father, the Son, and the Holy Spirit in the Holy Trinity and asserted that only the Son became incarnate as Jesus Christ. The Arian leaders were subsequently banished from their churches for heresy. The Emperor Constantine presided over the opening of the council and contributed to the discussion."
~from The History Channel