Hosius of Corduba (c. 257 – 359), also known as Osius or Ossius, was a bishop of Cordova and one of the prominent advocates of what became Catholic Christianity in the Arian controversy which divided the IV century early Christian Church. After Lactantius, he was the closest Christian advisor to the Emperor Constantine and guided the content of public utterances, such as Constantine's Oration to the Saints, addressed to the assembled bishops.
He was probably born in Roman Corduba (as it was then known) in Hispania, although a passage in Zosimus has sometimes been conjectured as the writer's belief that Hosius was a native of Egypt.
Elected to the see of Cordova before the end of the 3rd century, he narrowly escaped martyrdom in the persecution of Maximian (303-305). In 305 or 306 he attended the council of Illiberis or Elvira (his name appearing second in the list of those present), and upheld its severe canons concerning such points of discipline as the treatment of those who had abjured their faith during the recent persecutions, giving rise to the condemned rigorist position of Donatism and questions concerning clerical marriage.
In 313 he appears at the court of Constantine, being expressly mentioned by name in a constitution directed by the emperor to Caecilianus of Carthage in that year. In 323 he was the bearer and possibly the writer of Constantine's letter to Bishop Alexander of Alexandria and Arius his deacon, bidding them cease disturbing the peace of the church; and, on the failure of the negotiations in Egypt, it was doubtless with the active concurrence of Hosius that the Council of Nicaea was convened in 325. He certainly took part in its proceedings, and was one of the large number of confessors present; that he presided is a very doubtful assertion, as also that he was the principal author of the Nicene Creed. Still he powerfully influenced the eventual judgment of the emperor against the party of Arius.
After a period of quiet life in his own diocese, Hosius presided in 343 at the fruitless synod of Sardica, which showed itself so hostile to Arianism; there and afterwards he spoke and wrote in favour of Athanasius.
After Constantine's death, the prestige given to the orthodox cause in the Arianist controversy by the support of the venerable Hosius led the Arians to bring pressure to bear upon Constantius II, who had him summoned to Milan where he declined to condemn Athanasius nor to extend communion to Arians. He so impressed the emperor that he was authorized to return home. More Arian pressure led to Constantius writing a letter demanding whether he alone was going to remain obstinate. In reply, Hosius sent his courageous letter of protest against imperial interference in Church affairs (353), preserved by Athanasius[1] which led to Hosius' exile in 355 to Sirmium, an imperial center in Pannonia (in modern Serbia). From his exile he wrote to Constantius II his only extant composition, a letter justly characterized by the French historian Sebastian Tillemont as displaying gravity, dignity, gentleness, wisdom, generosity and in fact all the qualities of a great soul and a great bishop.
Subjected to continual pressure from the Arians the old man, who was near his hundredth year, was weak enough to sign the formula adopted by the third Council of Sirmium in 357,[2] which involved communion with the Arians but not the condemnation of Athanasius. He was then permitted to return to his Hispanic diocese, where he died in 359.
There is a letter from Pope Liberius to him (ca. 353).