ARIUS (d. 336), name celebrated in church history, not so much on account of the personality of its bearer as of the "Arian" controversy which he provoked (Gr. "Apaos). Our knowledge of Arius is scanty, and nothing certain is known of his birth or of his early training. We first hear of him as a deacon in Alex andria. After some controversy he was ordained presbyter by Achillas the Bishop, in 311, and discharged his duties with appar ent faithfulness and industry under Achillas, and afterwards under Alexander his successor. The cause of the controversy with which the name of Arius is associated lay not in any personalities but in a fundamental difference of doctrine which had far-reaching religious and philosophical implications. "Is the Divine," says Harnack, "which appeared on earth and made its presence actively felt, identical with the supremely Divine that rules heaven and earth? Did the Divine which appeared on earth enter into a close and permanent union with human nature, so that it has actually transfigured it and raised it to the plane of the Eternal?" Arius had received his theological education in the school of the presbyter Lucian of Antioch, a learned man, and distinguished especially as a biblical scholar. The latter was a follower of Paul of Samosata, bishop of Antioch, who had been excommunicated in 26g, but his theology differed from that of his master in a fundamental point. Paul, starting with the conviction that the One God cannot appear substantially on earth, and, consequently, that he cannot have become man in Jesus Christ, had taught that God had filled the man Jesus with his Logos (ao4la) or Power (815vaµis). Lucian, on the other hand, persisted in holding that the Logos became man in Christ. But since he shared the above-mentioned belief of his master nothing remained for him but to see in the Logos a second essence, created by God before the world, which came down to earth and took upon him self a human body. In this body the Logos filled the place of the intellectual or spiritual principle. Lucian's Christ, then, was not "perfect man," for that which constituted in him the personal element was a divine essence; nor was he "perfect God," for the divine essence was a created being. It is this idea which Arius took up and interpreted. His doctrinal position is explained in his letters to his patron Eusebius, bishop of the imperial city of Nicomedia, and to Alexander of Alexandria, and in the fragments of the poem in which he set forth his dogmas. From these writ ings it can even nowadays be seen clearly that the principal object which he had in view was firmly to establish the unity and simplicity of the eternal God. However far the Son may surpass other created beings, he remains himself a created being, to whom the Father before all time gave an existence formed "out of nothing" (E ovrt ovr.w). Arius was quite unconscious that his own monotheism was hardly to be distinguished from that of the pagan philosophers, and that his Christ was a demigod.
For years the controversy may have been fermenting in the college of presbyters at Alexandria. Sozomen relates that Alex ander only interfered after being charged with remissness in leav ing Arius so long to disturb the faith of the Church. According to the general supposition, the negotiations which led to the excommunication of Arius and his followers among the presbyters and deacons took place in 318 or 319. Arius was not without adherents, even outside Alexandria. Those bishops who, like him, had passed through the school of Lucian were not inclined to let him fall without a struggle, as they recognized in the views of their fellow-student their own doctrine, only set forth in a some what radical fashion. Eusebius of Nicomedia, a comrade of Arius in the school of Lucian, entered the lists energetically on his behalf. But Alexander, too, was active; by means of a circular letter he published abroad the excommunication of his presbyter, and the controversy excited more and more general interest.
It reached even the ears of Constantine. Now sole emperor, he saw in the one Catholic Church the best means of counter acting the movement in his vast empire towards disintegration; and he at once realized how dangerous dogmatic strife might prove to its unity. Constantine had no understanding of the questions at issue; and no course was left but to summon a gen eral or oecumenical council, which was convened in Nicaea (q.v.) in 325. After various turns in the controversy, it was finally decided, against Arius, that the Son was "of the same substance" (6 oovaios) with the Father, and all thought of his being created or even subordinate had to he excluded. Constantine accepted the decision of the council and resolved to uphold it. Alexander returned to his see triumphant, but died soon after, and was suc ceeded by Athanasius (q.v.), his deacon, with whose indomitable fortitude and strange vicissitudes the further course of the contro versy is bound up.
It only remains for us here to sketch what is known of the later career of Arius and the Arians. Although defeated at the council of Nicaea, the Arians were by no means subdued. Constantine, while strongly disposed at first to enforce the Nicene decrees, was gradually won to a more conciliatory policy by the influence especially of Eusebius of Caesarea and Eusebius of Nicomedia, the latter of whom returned from exile in 328 and won the ear of the emperor, whom he baptized on his death-bed. Athanasius was banished in 335. In 336, while awaiting readmis sion to the church, Arius was suddenly taken ill while walking in Constantinople, and died in a few moments. His death seems to have exercised no influence worth speaking of on the course of events. His theological radicalism had in any case never found many convinced adherents. It was mainly the opposition to the Homoousios, as a formula open to heretical misinterpretation, and not borne out by Holy Writ, which kept together the large party known as Semiarians, who carried on the strife against the Nicenes and especially Athanasius. Under the sons of Con stantine Christian bishops in numberless synods cursed one another turn by turn. In the western half of the empire Arian ism found no foothold, and even the despotic will of Constantius, sole emperor after 351, succeeded only for the moment in sub duing the bishops exiled for the sake of their belief. In the east, on the other hand, the Semiarians had for long the upper hand. They soon split up into different groups, according as they came to stand nearer to or farther from the original position of Arius. The actual centre was formed by the Homoii, who only spoke generally of a likeness Ru mor77s) of the Son to the Father; to the left of them were the Anomoii, who, with Arius, held the Son to be unlike (avo/Amos) the Father; to the right, the Ho moousians who, taking as their catchword "likeness of nature" (Oµ0corrls rtar' oboiav), thought that they could preserve the re ligious content of the Nicene formula without having to adopt the formula itself. Since this party in the course of years came more and more into sympathy with the representatives of the Nicene party, the Homoousians, and notably with Athanasius, the much-disputed formula became more and more popular, till the council summoned in 381 at Constantinople, under the auspices of Theodosius the Great, recognized the Nicene doctrine as the only orthodox one. Arianism, which had lifted up its head again under the emperor Valens, was thereby thrust out of the state Church. It lived to flourish anew among the Germanic tribes at the time of the great migrations, but here too as a distinctive na tional type of Christianity it perished before the growth of me diaeval Catholicism, and the name of Arian ceased to represent a definite form of Christian doctrine within the Church, or a definite party outside it.
See H. M. Gwatkin, Studies of Arianism (2nd ed., 190o) ; Harnack, History of Dogma, Eng. tr., vol. iv.; Hastings, Encyclopaedia of Religion and Ethics, art. "Arianism." The religious and philosophical aspect of the question is discussed in Mellone, The Price of Progress (1924), ch. iv.