ARIO. – Heresiarch, Arianism (v.), born in 256 in Libya, died in 336 at Constantinople. A disciple, it seems, of Luciano d'Antiochia, nothing is known of his life before 306, when he took part in the Meletian schism at Alexandria. He separated from it shortly thereafter, and about 308 received the diaconate from Bishop Pietro of Alexandria. The severity shown by the latter toward the Meletians drove A. into opposition, and he did so much that the bishop excommunicated him. It was only under his successor Achilla that he was reconciled with the Church and ordained a priest (312). In 313 he was at the head of a church in Alexandria called Baucali, where his name soon became popular. His contemporaries who have transmitted his portrait describe him as tall and spare in build, austere in his ways, attractive in appearance, learned and a skilled dialectician, but proud and eager for domination, cunning and insincere.
For several years he lived in harmony with Alessandro, Achilla's successor in the episcopate, but between 318 and 320 (according to others, 323) the first disagreements broke out concerning the consubstantiality of the Word. In explaining Scripture in his church at Baucali, A. advanced theories in which the teaching of Luciano d'Antiochia was making its way, with all that it implied in terms of subordination and exegetical and dialectical tendencies opposed to those prevailing in Alexandria. Basically, A. denied the divinity of the Word, presenting him as a secondary god, substantially different from the Father, who had created him from nothing and by a free act of will. After having shown patience, Bishop Alessandro rejected A.'s conceptions; A., heedless of the condemnation, went in search of support among the episcopate. Against the epistolary campaign unleashed by the rebel, the bishop of Alexandria responded with countermeasures, and at the same time had the priest of Baucali and his adherents condemned by a synod of 100 bishops assembled in his city. Since his continued residence in Alexandria had become impossible, A. sought refuge with his powerful protector, Bishop Eusebio di Nicomedia, who had a synod declare his friend's doctrine orthodox. This success won him further support: from Bishop Eusebio di Cesarea he obtained the convocation of a synod that agreed to intervene with Alessandro by requesting A.'s reinstatement. During his stay in Nicomedia, A. wrote his principal work, entitled Thalia (the banquet), of which only fragments remain, transmitted by s. Atanasio (Oratio I contra Arianos: PG 26, 16-33; De Synodis, 15: ibid., 26, 705, etc.); it was composed, it seems, partly in prose and partly in verse, according to the metre of the Egyptian poet Sótades. A. chose this light form in order to make the doctrine he advocated familiar to the masses. Eusebio di Nicomedia, full of zeal for his fellow-Lucianist, also enlisted the support of the emperor's sister, Costanza. Soon Costantino himself became interested in the conflict, and in a letter urging concord he censured the conduct of Alessandro and A. for having raised useless questions. To restore peace and unity, he summoned an ecumenical council at Nicea. The 300 bishops who took part in it in 325 condemned A. and his doctrine. But he refused to sign the creed, and Costantino exiled him to Illyricum together with a few recalcitrant supporters.
Whatever the disagreement among historians concerning the later events, a change did take place in Costantino's conduct toward the Arians. After several years, under the influence of his sister Costanza and Eusebio di Nicomedia, Costantino decided to recall the exiles. The opposition of s. Atanasio did not prevent the rehabilitation of A., decreed at the Council of Jerusalem (335) following a profession of faith issued by him and judged orthodox by his supporters. Thus, while the patriarch of Alexandria was taking the road into exile, A. entered the city in triumph. But the people, faithful to Atanasio, rose up against him, and the alarmed emperor summoned him to Constantinople, where, urged on by the Eusebians, he ordered the bishop of the capital to receive A. into communion with the Church. But on the eve of the ceremony, which was to take place in the basilica of the Holy Apostles, A. was struck by sudden death while crossing the streets of the city, followed by a crowd of adherents (s. Atanasio, De morte Arii: PG 25, 685-90).