When and where was the first ecumenical council held?

The first ecumenical council is recognized as the Council of Nicaea, which was held in AD 325. This significant event took place in Nicaea, which is located in present-day Turkey. This council was convened by Emperor Constantine with the primary goal of addressing and settling various controversies that arose in the early Christian community, particularly concerning the nature of Christ and His relationship to God the Father.

The Council of Nicaea produced the Nicene Creed, a statement of faith that affirmed the divinity of Jesus Christ and established foundational Christian beliefs that continue to shape Christian doctrine today. The formation of this creed was crucial in combating Arianism, a theological position that denied the full divinity of Jesus. The decisions made at Nicaea had lasting effects, leading to a unified Christian doctrine and promoting a more organized church structure.

In contrast to this, other councils mentioned in the choices occurred later in the history of the church and built upon the decisions made at Nicaea, hence being significant but not recognized as the first ecumenical council.