The Council of Nicaea and the Shaping of the Creed
Emperor Constantine summoned roughly 300 bishops to Nicaea in 325 AD to settle the Arian controversy — producing the Nicene Creed and a unified statement on the divinity of Christ.
In May 325 AD the Roman Emperor Constantine I summoned bishops from across the empire to the lakeside town of Nicaea in Bithynia (modern İznik, Turkey). Roughly 300 bishops attended — most from the Greek-speaking East, with a handful from the Latin West and at least one bishop from Persia.
The central question was the teaching of Arius, an Alexandrian presbyter who held that the Son of God was a created being, subordinate to and lesser than the Father. Athanasius, then a young deacon, led the opposition. After weeks of debate the council produced a statement of faith — the original Nicene Creed — that affirmed the Son as "of the same substance" (homoousios) with the Father.
Nicaea also fixed the calculation of Easter, regularised episcopal jurisdictions, and produced 20 canons on church discipline. The creed itself was expanded at the First Council of Constantinople (381 AD) into the version still recited in churches today.