Constantine's role in calling the Council of Nicaea has long been recognized. But theological interests have overshadowed the political side of his decision-making. In the nineteenth century scholars coined the word “Caesaropapism” for imperial interference that they saw as a threat to the purity of the Church. But the ancient state operated on a different set of principles, and a political approach fills in important blanks in our understanding of the council. By the time Constantine took control of the eastern empire he had learned that the best way to deal with conflict in the Church was to assemble the largest number of bishops possible and have them settle the problem. This is the thinking behind his decision to ask all the bishops in the empire to settle the Arian question. This is why Nicaea became known as the first ecumenical (“world-wide”) council, though in reality almost all of the bishops present came from the East. Publicly, Constantine treated the bishops at Nicaea with respect and humility, but behind the scenes he worked to bring the opposing parties into agreement. The result was the Nicene Creed, still recited (in slightly different form) by Christians today.

The main acts of Nicaea were gradually reversed over the years 327-60. Constantine honored its name and canons throughout his life, but recalled Arius from exile, leaned on church leaders to restore him to communion, and sidelined Arius’s opponents. Constantius II flouted Nicaea’s canons and officially replaced its creed. Nonetheless, Nicaea’s pronouncements on the Son’s relationship to the ousia of the Father, including the term homoousios, which had been a response to Eusebius of Nicomedia’s Letter to Paulinus of Tyre, continued to be debated throughout this period in a succession of mutually allusive theological works. These include Eusebius of Caesarea’s Letter to his Church, Eustathius of Antioch’s Against the Arian Madness, Asterius the Sophist’s Defence of Eusebius of Nicomedia, Marcellus of Ancyra’s Against Asterius, Eusebius’s Against Marcellus and On Ecclesiastical Theology, Acacius of Caesarea’s Against Marcellus, Marcellus’ Letter to Julius of Rome, Athanasius’s Orations Against the Arians, the Profession of Faith of Sirmium 351, and Athanasius’s On the Decrees of Nicaea. The last of these, together with his formidable political skills, established the Nicene Creed against all the odds as the only formula which was able to command widespread support among bishops across the empire after the death of Constantius.

During the formative period of disputation over the theology of Arius, the emperor Licinius ruled over the eastern Roman provinces. The emperor Constantine was directly involved in the doctrinal controversy only after his victory over Licinius in 324. But Constantine’s engagement in imperial politics had already shaped his thinking about theology. In imperial successions sons were sometimes promoted but also sometimes overlooked. Emperors introduced a new five-year cycle for calculating taxes and often held annual consulships. Emperors identified with deities such as Jupiter and Hercules. At the Council of Nicaea, Constantine was hence ready to debate with bishops over the theology of Father and Son, the annual date of Easter, and the simultaneous divinity and humanity of Jesus Christ. One bishop who attended the council was Eusebius of Caesarea, whose panegyric equated the emperor with the Son of God. Constantine himself strengthened the association by funding churches in honor of Jesus’s nativity and resurrection in the Holy Land and by publicizing a story about his own vision of a cross in the sky. The Council of Nicaea had been a crucible for the formation of both a theology of God and a political philosophy of a Christian emperor.