HOSIUS or Osius (c. 359), bishop of Cordova, was born probably at Cordova. He was elected to that see before the end of the 3rd century and narrowly escaped martyrdom in the persecution of Maximian (303-305). In 305 or 3o6 he attended the council of Illiberis or Elvira, and upheld its severe canons concerning the treatment of the lapsed and clerical marriages. In 313 he appears at the court of Constantine, and io years later, as the bearer of Constantine's letter to Bishop Alexander of Alexandria and Arius his deacon, bidding them cease disturbing the peace of the church. He was present at the council of Nicaea in 325, and powerfully influenced the judgment of the emperor in favour of the orthodox party. Hosius presided in 343 at the fruitless synod of Sardica, which showed itself so hostile to Arianism ; and afterwards he supported Athanasius in such a way as to bring upon himself a sentence of banishment to Sirmium (355). From his exile he wrote to Constantius II. a letter now his only extant composition. Under pressure, he signed the for mula adopted by the second synod of Sirmium in 357, which involved communion with the Arians but not the condemnation of Athanasius. He was then permitted to return to his diocese, where he died in 359.
See S. Tillemont, Memoires, vii. (1700) ; Hefele, Conciliengeschichte (2nd ed., 1873, etc.), vol. i.; H. M. Gwatkin, Studies of Arianism (1882, 2nd ed., 'goo) ; A. W. W. Dale, The Synod of Elvira (i882) ; Duchesne, Histoire ancienne de l'Eglise (1908), and Herzog-Hauck, Realencvklopddie (3rd ed., 'goo).