Historical Development of the Trinity Doctrine – Fifth Century Arianism

The religious preferences of the Roman Emperors determined the Christology of the church. Emperor Constantine had a huge role in the formulation of the Nicene Creed. During the next 50 years, the emperors Constantius and Valens enforced Arianism. In 380 Theodosius became emperor and immediately outlawed Arianism. In the fifth century, Arian Germanic immigrants dominated the Western Empire and the West was Arian once again. But they tolerated the Roman Church and it actually grew in strength.

Emperor Theodosius wiped out Arianism among the Roman people in 380.

When Theodosius I became emperor, the imperial capital was solidly Arian. Commentators often refer to the council of Constantinople of 381 as the turning point where Arianism was replaced by Nicene Christology, but that council was a mere formality. Already prior to the council, Theodosius outlawed all other forms of Christianity and exiled Arian bishops. Furthermore, Arians were not allowed to attend the Council of 381. The 381 Council, therefore, was simply a formality. The real decisions were taken by the Roman Emperor.