ers of the Holy
Trinity; God the Father, the Son, and the Spirit. About 318 A. D., Arius,
a presbyter of Alexandria, taught that God was from eternity but that the
Son and the Spirit were his creations. Over the teaching of Arius, a
controversy arose which threatened the unity of the church. Accordingly,
Constantine intervened and summoned the ecumenical council of Nicaea to
decide upon the orthodoxy of Arius. The council accepted the formula of
Athanasius that the Son was of the same substance (_homo-ousion_) as the
Father, which was the doctrine of the West. Arius was exiled.

The struggle, however, was by no means over, for the Nicene creed found
many opponents among the eastern bishops who did not wish to exclude the
Arians from the church. The leader of this party was Eusebius of Caesarea.
In 335 they brought about the deposition of Athanasius, who had been
bishop of Alexandria since 328. After the death of Constantine, Athanasius
was permitted to return to his see, only to be expelled again in 339 by
Constantius, who was under the influence of Eusebius. He took refuge in
the West, where the Pope Julius gave him his support. At a general council
of the church held at Serdica (Sofia) in 343 there was a sharp division
between East and West, but the supporters of Athanasius were in the
majority, and he and the other orthodox eastern bishops were reinstated in
their sees (345 A. D.).

When Constantius became sole ruler of the empire (353 A. D.) the enemies
of Athanasius once more gained the upper hand. The emperor forced a
general council convoked at Milan in 353 to condemn and depose Athanasius,
while the Pope Liberius, who supported him, was exiled to Macedonia. A new
council held at Sirmium in 357 tried to secure religious peace by
forbidding the use of the word "substance" in defining the relation of the
Father and the Son, and sanctioned only the term _homoios_ (like). The
adherents of this creed were called Homoeans. Although they were not
Arians, their solution was rejected by the conservatives in both East and
West. In 359 a double council was held, the western bishops meeting at
Ariminum, the eastern at Seleucia. The result was the acceptance of the
Sirmian creed, although the western council had to be almost starved
before it yielded. Under Julian and Jovian the Arians enjoyed full
toleration, and while Valentinian I pursued a similar policy, Valens went
further and gave Arianism his support.

In the meanti