The first Council of Nicaea (Council I) was convened in 325 AD. It was the first time Christianity could be called together from across the Roman Empire as it had been illegal before then and suffered persecutions leading to death. The council condemned Christian heresies that denied the divinity of Jesus Christ, especially Arianism. The Council affirmed that Jesus was the Son of God. The Council issued the Nicene Creed, which codified the theological understanding of the Holy Trinity and remains the unified statement of faith of all Christians to this day.
The Council was presided over by the EmporerConstantine, who is said to have coined the term homousis, the current language in the Nicene Creed describing Jesus as "of the same substance" as the father. The Council of Nicaea also canonized the current Bible, agreeing to the form that had been in common usage.