Arianism:A brief history.

 Arianism is a Christological doctrine first attributed to Arius (c. AD 256–336), a Christian presbyter in Alexandria, Egypt. Arian theology holds that Jesus Christ is the Son of God. who was begotten by God the Father. The Arian concept of Christ is based on the belief that the Son of God did not always exist but was begotten within time by God the Father, therefore Jesus was not co-eternal with God the Father. Arianism holds that the Son is distinct from the Father (and therefore subordinate to Him).

The term Arian is derived from the name Arius; it was not what the followers of Arius's teachings called themselves, but rather a term used by outsiders. The nature of Arius's teachings and his supporters were opposed to the theological doctrines held by Homoousian Christians, regarding the nature of the Trinity and the nature of Christ.

There was a controversy between two interpretations of Jesus' divinity (Homoousianism and Arianism) based upon the theological orthodoxy of the time, one Trinitarian and the other also a derivative of Trinitarian orthodoxy, and both of them attempted to solve its respective theological dilemmas. The former was formally affirmed by the first two ecumenical councils; since then, Arianism has always been condemned as "the heresy or sect of Arius". As such, all mainstream branches of Christianity now consider Arianism to be heterodox and heretical. Trinitarian (homoousian) doctrines were vigorously upheld by Patriarch Athanasius of Alexandria, who insisted that Jesus (God the Son) was "same in being" or "same in essence" with God the Father. Arius stated: "If the Father begat the Son, then he who was begotten had a beginning in existence, and from this it follows there was a time when the Son was not." The ecumenical First Council of Nicaea of 325, convened by Emperor Constantine to ensure church unity, declared Arianism to be a heresy. According to Everett Ferguson, "The great majority of Christians had no clear views about the nature of the Trinity and they did not understand what was at stake in the issues that surrounded it."

Ten years later, however, Constantine the Great, who was himself later baptized by the Arian bishop Eusebius of Nicomedia in 337 AD, convened another gathering of church leaders at the regional First Synod of Tyre in 335 (attended by 310 bishops), to address various charges mounted against Athanasius by his detractors, such as "murder, illegal taxation, sorcery, and treason", following his refusal to readmit Arius into fellowship. Athanasius was exiled to Trier (in modern Germany) following his conviction at Tyre of conspiracy, and Arius was, effectively, exonerated. Athanasius eventually returned to Alexandria in 346, after the deaths of both Arius and Constantine. Though Arianism had spread, Athanasius and other Nicene Christian church leaders crusaded against Arian theology, and Arius was anathemised and condemned as a heretic once more at the ecumenical First Council of Constantinople of 381 (attended by 150 bishops). The Roman Emperors Constantius II (337–361) and Valens (364–378) were Arians or Semi-Arians, as was the first King of Italy, Odoacer (433?–493), and the Lombards were also Arians or Semi-Arians until the 7th century. Visigothic Spain was Arian until 589. Many Goths adopted Arian beliefs upon their conversion to Christianity. The Vandals actively spread Arianism in North Africa.

Arianism is also used to refer to other nontrinitarian theological systems of the 4th century, which regarded Jesus Christ—the Son of God, the Logos—as either a begotten creature of a similar or different substance to that of the Father, but not identical (as Homoiousian and Anomoeanism) or as neither uncreated nor created in the sense other beings are created (as in semi-Arianism).