Ὅσιος, (i. e. Holy), sometimes written O'SIUS, an eminent Spanish ecclesiastic of the fourth century. As he was above a century old at the time of his death, his birth cannot be fixed later than A. D. 257, and is commonly fixed in 256. That he was a Spaniard is generally admitted, though if he be (as Tillemont not unreasonably suspects), the person mentioned by Zosimus (2.29), he was an Egyptian by birth. That he was a native of Corduba (Cordova) is a mere conjecture of Nicolaus Antonio. As he held the bishopric of Corduba above sixty years, his elevation to that see was not later than A. D. 296. He assisted at the council of Iliberi or Eliberi, near Granada, and his name appears in the Acta of the council as given by Labbe. (Concil. vol. i. col. 967, &c.) The date of this council is variously computed. Labbe fixes it in A. D. 305, and Cave follows him; but Tillemont contends for A. D. 300. Hosius suffered, as his own letter to the emperor Constantius shows, in the persecution under Diocletian and Maximian, but to what extent, and in what manner, is not to be gathered from the general term "confessus sum," which he uses. The reverence which his unsullied integrity excited was increased by his endurance of persecution ; and he acquired the especial favour of the emperor Constantine the Great. In A. D. 324 Constantine sent him to Alexandria with a soothing letter, in which he attempted to stop the disputes which had arisen between Alexander, the bishop of Alexandria, and the presbyter Arius. [ALEXANDER, ST. p. 111; ARIUS.] He was also instructed to quiet, if possible, the disputes which had arisen as to the observance of Easter. The choice of Hosius for this conciliatory mission, which, however, produced no effect, shows the opinion entertained by the emperor of his moderation and judgment.

In A. D. 313 he seems to have been concerned in the distribution of money made by Constantine to the churches in Africa (Euseb. Hist. Eccl. 10.6.) : perhaps it was owing to something which occurred on this occasion, that he was accused by the Donatists of having assisted Caecilianus in persecuting them, and of having instigated the emperor to severe measures against them. They also affirmed that he had been condemned on some charge not stated by a synod of Spanish bishops, and absolved by the prelates of Gaul. Augustin (Contra Epistolam Parmeniani, 1.7) virtually admits the truth of this statement; and, from the nature of the Donatist controversy, it is not improbable that the charge was of some unworthy submission during the persecution of Diocletian--a charge not inconsistent with the closing incident in the career of Hosius.

Hosius certainly took part in the council of Nicaea (Nice) A. D. 325; and, although the earlier writers, Eusebius, Sozomen, and Socrates give no ground for the assertions of Baronius (Annal. Eccles. ad ann. 325, xx.) that Hosius presided, and that in the character of legate of the pope, who was absent, and even Tillemont admits that the proofs of these assertions are feeble, yet it is remarkable that the subscription of Hosius in the Latin copies of the of the council stands first; and Athanasius says that he usually presided in councils, and that his letters were always obeyed. Perhaps also his presidency may be intimated in what Athanasius (Histor. Arian. ad Monach. 100.42) makes the Arian prelates say to Constantius, that Hosius had published the Nicene creed (τὴν ἐν) Νικαίᾳ πίστιν ἐξέθετο), an expression which Tillemont interprets of his composing the creed. We hear little of Hosius until the council of Sardica, A. D. 347, where he certainly took a leading part, and at which probably he was again president. In A. D. 355 Constantius endeavoured to persuade Hosius to write in condemnation of Athanasius, and the attempt, which was not successful, drew from the aged bishop a letter, the only literary remain which we have of him, which is given by Athanasius (Hist. Arian. ad Monach. 44). Constantius sent for Hosius to Milan A. D. 355, in hopes of subduing his firmness, but not succeeding, allowed him to return. In 356-7 the emperor made a third trial, and with more success. He compelled Hosius to attend the council of Sirmium; kept him there for a year in a sort of exile (Athanas. ut sup. 100.45), and, according to the dying declaration of the old man, confirmed by Socrates, had him subjected to personal violence. Hosius so far submitted as to communicate with the Arian prelates Valens and Ursacius, but could not be brough t to condemn Athanasius, and with this partial submission his persecutors were obliged to be content. (Athanas. l.c.) This was in 357, and he was dead when Anathasius wrote the account of his sufferings a year after. The manner of his death is disputed. An ancient account states that while pronouncing sentence of deposition on Gregory of Iliberi, who had refused, on account of his prevarication at Sirmium, to communicate with him, he died suddenly. His memory was regarded differently by different persons; Athanasius eulogises him highly, and extenuates his tergiversation; Augustin also defends him.