Aerius, Ἀέριος , founder of the heretical sect of the Aerians , c. 355, still living when Epiphanius wrote against heresies, 374–376. He was the early friend and fellow-disciple of Eustathius of Sebaste in Pontus. While they were living an ascetic life together, the bishopric of Sebaste became vacant. Each of the friends was a candidate for the office. The choice fell on Eustathius. This was never forgiven by Aerius. Eustathius endeavoured to soften his friend's disappointment by at once ordaining Aerius presbyter, and setting him over the hospital established at Sebaste ( ξενοδοχεῖον , or πτωχοτροφεῖον ). But all his attempts were fruitless. Aerius threw up his charge, deserted the hospital, and openly published grave accusations against his bishop. The rupture with Eustathius widened into a rupture with the church. Aerius and his numerous followers openly separated from their fellow-Christians, and professed ἀποταξία , or the renunciation of all worldly goods. They were consequently denied not only admission to the churches, but even access to the towns and villages, and they were compelled to sojourn in the fields, or in caves and ravines, and hold their religious assemblies in the open air exposed to the severity of Armenian winters.

Our knowledge of Aerius is from Epiphanius (Haer. 75). Augustine, de Haeresibus, c. 53, merely epitomises Epiphanius. Aerius went so fearlessly to the root of much that the church was beginning to cling to, that we cannot feel much surprise at the vehemence of Epiphanius with regard to his teaching.

Epiphanius asserts that he went beyond Arius in his impieties, specifying four counts. (1) The first with which the name of Aerius has been chiefly identified in modern times is the assertion of the equality of bishops and presbyters, μία τάξις, μία τιμή. ἕν ἀξίωμα . (2) Aerius also ridiculed the observance of Easter as a relic of Jewish superstition. (3) Prayers and offerings for the dead he regarded as pernicious. If they availed for the departed, no one need trouble himself to live holily: he would only have to provide, by bribes or otherwise, a multitude of prayers and offerings for him, and his salvation was secure. (4) All set fasts he condemned. A Christian man should fast when he felt it to be for his soul's good: appointed days of fasting were relics of Jewish bondage. Philaster, whose unconfirmed authority is very small, confounds the Aerians with the Encratites, and asserts that they practised abstinence from food and rejected marriage (Philast. Haer. 72). Consult Schröckh, Christliche Kirch. Gesch. vol. vi. pp. 226–234; Walch, Ketzerhist. vol. iii. pp. 221 seq.; Neander, Ch. Hist. vol.iii. pp. 461–563 (Clark's trans.); Herzog. Real-encycl. vol. i. 165; Tillemont, Hist. eccl . vol. ix. pp. 87 seq.

[E.V.]