By the 4th century, subordinationism was "regarded as clearly heretical in its denial of the co-equality of the Three Persons of the Trinity. The issue was most explicitly dealt with in the conflict with Arius and his followers, who held that the Son was God not by nature but by grace and was created by the Father, though in a creation outside time." Subordination of the Holy Spirit became more prominent in the 4th century Pneumatomachi. The second ecumenical council, Constantinople I, condemned subordinationism in 381.