The First Council of Nicaea, called by Emperor Constantine I, commenced in the city of Nicaea, located in present-day Turkey. This significant gathering of Christian bishops was primarily convened to address pressing theological controversies that had arisen within the Church, particularly regarding the nature of Christ and the Arian controversy. Led by Constantine, the council sought to unify the diverse and often conflicting beliefs among Christians to establish a cohesive doctrine that could be uniformly accepted across the Roman Empire.

One of the main subjects of deliberation was the Arian position, founded by Arius, which posited that Christ was a created being and not co-eternal with the Father. This directly challenged the doctrine of the Trinity, which held that Jesus Christ was divine and of one substance with God the Father. The council ultimately condemned Arianism and produced the Nicene Creed, a statement of faith that affirms the divinity of the Son, establishing essential Christian orthodoxy.

Furthermore, the council addressed other pivotal matters, including the date of Easter and various ecclesiastical regulations concerning church governance and conduct. The Nicene gatherings became a model for future ecumenical councils and crucially shaped the development of Christian theology and unity within the Church, setting a historical precedent for addressing doctrinal disputes.