This year marks the 1700th anniversary of the “Council of Nicaea” famous for being the first-ever “ecumenical” gathering of Christian leaders the town of Nicaea (now Iznik in modern Türkiye) in 325.

Around the world commemorative celebrations, conferences, and other opportunities to reflect upon and learn about this Council and the (later) Nicene Creed that developed from it are taking place. What was Nicaea all about?

Christianity, for its first three hundred years or so, was one among many religions within the Roman empire. Christians were at best tolerated. From time to time, they suffered persecution. Persecution produced martyrs.

Martyrs were those who suffered and died for their faith. The last major persecution was inaugurated by the emperor Diocletian, in 303 CE. He died a couple of years later, by which time the empire had four emperors – two in the West and two in the East. This was the “tetrarchy” structure that Diocletian had set up. It didn’t last for very long. Both Western emperors were rivals for their half of the Roman empire. In 312 CE the one who triumphed was Constantine, who eventually went on to rule the whole empire.

Constantine’s victory was a turning point for Christians. He favoured Christianity, although he waited until the end of his life before being baptised. In the year 313 Constantine promulgated the “Edict of Milan”, a declaration of toleration that gave freedom of religion to all. Importantly, it gave favoured status to the Christians to whom confiscated churches and possessions from the Diocletian persecution were restored.

Christianity, once persecuted by the empire, now had imperial support. Constantine even bestowed villas and palaces upon Christian bishops. He regarded the Christian religion as good for the empire. But the empire needed something in return: the stable support of a fast-growing, united, Christian Church. And this required religious stability.

However, within a decade, by the early 320s, a theological controversy threatened to split the Church. Since the earliest days the Church had fought hard to ensure its “catholicity” (universality), its “orthodoxy” (correct belief) and its unity (its organisational “oneness”). A controversy that risked schism, a fracturing of unity, was a very serious matter, one that the emperor was at pains to avoid. For such a split would have political consequences.

What was the theological problem? It was the question of the status of Christ, God the Son, relative to God the Father. Did this not mean there were two gods? It seemed to.

The issue had been highlighted by Arius, a priest and theologian at Alexandria, one of the emerging vibrant and influential centres of Christianity. In his view, the fact that Jesus was born the son of God the Father implied that Christians worship two separate divine beings – one senior (Father) and one junior (Son).

Furthermore, as with all father–son relationships, the elder is superior and the junior is subordinate. Also, God the Father is transcendent and eternal – that is, outside the realm of space and time – and the Son is immanent, meaning within both space and time. The two can’t be equated as being “the same”, nor on the same level in terms of divinity. Thus, for Arius, and those who followed him, God the Son was doubly subordinate (both “junior” and “in time”).

Christ was therefore a divine being, a kind of “demi-god”, but not the same as the Father and Creator of all.

There were many who opposed this Arian thinking. The issue of the divinity of the Son needed resolving. Emperor Constantine convened, and hosted, the meeting at Nicaea of 318 bishops from around the empire to do just that.

As it happened, theological debate at Nicaea dragged on, with neither side willing to compromise. Something had to happen to break the impasse. Emperor Constantine weighed in. He favoured the line of opposition to Arius as articulated by another theologian from Alexandria, Athanasius, supported by his bishop. This likely helped. In the end, the statement, or “creed” of Nicaea was imposed by imperial decree.

It asserted the unity of God (Father and Son). They are of the “same substance” (Greek homoousios), not just similar, or “like” substances (homoiousios). The first two clauses of the “Creed of Nicaea” spell this out. Jesus Christ is “very God of very God”.

The third and final one-line clause simply states belief in the Holy Spirit. The divinity, and so inclusion, of the Spirit as integral to the Christian idea of God did not come about until the full Nicene Creed, with its emphatic declaration of Tri-unity or trinitarianism, was finalised at the Council of Constantinople in 381CE. What Nicaea began, Constantinople finished.

The initial creed of Nicaea was not used liturgically. It was intended, rather, as a theological guide for the use of bishops only, to inform their teaching and so ensure doctrinal uniformity.

Furthermore, the Nicaea statement included an additional clause: the Anathema. This, aimed at bishops and priests, said in effect that anyone who did not believe or assent to this “sound doctrine” would be banished as heretics from the Roman empire. There were dire consequences in those days for anyone who did not conform to “orthodox” (that is, correct or right) belief.

The outcome of the Council of Nicaea marks the beginnings of the Church gaining state sanction to silence and remove opposition and dissent, something that has recurred throughout Christian history since. It is a most important milestone in the development of both Christian faith as such, and the Church as an organisation. Its effects can be traced to today, wherever the Church is able to draw upon the forces and sanctions of the state for its own purposes and, contrariwise, where the State calls upon the Church to endorse its policies and actions.

As noted above, the Nicene Creed was begun at Nicaea but not completed for another 56 years, at the Second Ecumenical Council (381 CE). This was held at the newly formed city of Constantinople (formerly Byzantium, later renamed Istanbul). The full title of the Nicene Creed is the “Niceno-Constantinopolitan Creed”. Quite a mouthful! Everyone uses the short title.

Today, not all Christians may have encountered the Nicene Creed. Not all churches use it regularly in worship, if at all. In some churches the Creed is recited frequently; for others it is a bit now and then. Yet it is this creed that encapsulates the uniqueness of Christian belief in distinction from other theistic beliefs. Christianity holds that the one God is understood to comprise three equal “persons” – Father, Son and Holy Spirit – that are distinct centres of identity and relationality, but not separate divine beings. If that were the case, Christianity would be a polytheistic, not a monotheistic, faith.

The Council of Nicaea was certainly a defining moment in Christian history. Its principal task was to deal with a major theological controversy. It also determined the date of Easter. It marked the development of a formal and mutual relationship of Christianity and the empire; a significant moment in the history of Church–State relations. It had a huge impact on the development of Christianity and its effects can be traced down to 2025.