Commemorated on August 27
St. Hosius (ca. 256-358) was probably born in Roman Cordova, Spain although there is belief that he was a native of Egypt. He lived a life true to his name which means "holiness" (Greek). He was bishop of Cordova for more than sixty years during the fourth century. St. Hosios served as ecclesiastical adviser (312-326) to Emperor Constantine the Great, and was one of the main defenders of Orthodoxy in the West against the early Donatists and in the Arian controversy, which divided the fourth century early Christian Church. St. Hosios advised Constantine to convene the First Ecumenical Council in Nicea (325), and he was the first to sign the acts of this Council.
St. Hosios was concentrated bishop of Cordova (295) and was nearly martyred in the persecution of Maximian (303-305). He attended the council of Elvira (Granada) in 305 and 306 where he upheld canons concerning such points of discipline as the treatment of those who had abjured (lapsed) their faith during the recent persecutions and questions concerning clerical marriage.
St. Hosios convoked a synod at Alexandria of Egyptian bishops and another at Antioch of Syrian bishops, at both of which Arius and his followers were condemned. He presided at the Council of Sardica (now Sophia in Bulgaria), where he spoke and wrote in favour of Athanasius of Alexandria, a principal opponent of Arianism.
The Arians pressured Emperor Constantine to summon St. Hosios to Milan where St. Hosios refused to condemn Athanasius nor to extend communion to the Arians. Constantine was so impressed that St. Hosios was authorized to return home.
Under Arian pressure, Constantine wrote a letter demanding whether St. Hosios was going to remain obstinate. St. Hosios sent a letter of protest against imperial interference in Church affairs (353) which led to St. Hosios' exile and detainment in 355 to Sirmium, in Pannonia (in modern Serbia).
Under threats and physical violence, St. Hosios (nearly 100 years old) signed the Arian formula of Sirmium (357). Then and only then was he permitted to return to his diocese in Córdoba, but he retracted his signature before he died.
Alternate spelling: Hosius, Osios, Osius.