Arius lived and taught in Alexandria, Egypt, in the early 4th century. The most controversial of his teachings dealt with the relationship between God the Father and the person of Jesus, saying that Jesus was not one with the Father, and that he was not fully, although almost, divine in nature. This teaching of Arius conflicted with trinitarian christological positions which were held by the Church (and subsequently maintained by the Roman Catholic Church, the Eastern Orthodox Churches and most Protestant Churches).
The term "Arianism" is also used to refer to other nontrinitarian theological systems of the fourth century, which regarded the Son of God, the Logos, as a created being (as in Arianism proper and Anomoeanism) or as neither uncreated nor created in the sense other beings are created (as in "Semi-Arianism").
Of all the various disagreements within the Christian Church, the Arian controversy has held the greatest force and power of theological and political conflict, with the possible exception of the Protestant Reformation. The conflict between Arianism and Trinitarian beliefs was the first major doctrinal confrontation in the Church after the legalization of Christianity by the Roman Emperor Constantine I.
The controversy over Arianism began to rise in the late third century and extended over the greater part of the fourth century and involved most church members, simple believers, priests and monks as well as bishops, emperors and members of Rome's imperial family. Yet, such a deep controversy within the Church could not have materialized in the third and fourth centuries without some significant historical influences providing the basis for the Arian doctrines. Most orthodox or mainstream Christian historians define and minimize the Arian conflict as the exclusive construct of Arius and a handful of rogue bishops engaging in heresy. Of the roughly three hundred bishops in attendance at the Council of Nicea, only three bishops did not sign the Nicene Creed.
After the dispute over Arius politicized the debate and a catholic or general solution to the debate was sought, with a great majority holding to the trinitarian position, the Arian position was declared officially to be heterodox. There is some irony in that the Roman Catholic Church canonized Lucian of Antioch as a brilliant and talented early Christian leader and martyr, although Lucian taught a very similar form of what would later be called Arianism. Arius was a student of Lucian's private academy in Antioch. The Ebionites, among other early Christian groups, also may have maintained similar doctrines that can be associated with formal Lucian and Arian Christology.
While Arianism continued to dominate for several decades even within the family of the Emperor, the Imperial nobility and higher-ranking clergy, in the end it was Trinitarianism which prevailed politically and thus theologically in the Roman Empire at the end of the fourth century. Arianism, which had been taught by the Arian missionary Ulfilas to the Germanic tribes, was dominant for some centuries among several Germanic tribes in western Europe, especially Goths and Lombards (and significantly for the late Empire, the Vandals), but ceased to be the mainstream belief by the 8th Century AD. Trinitarianism remained the dominant doctrine in all major branches of the Eastern and Western Church and within Protestantism, although there have been several anti-trinitarian movements, some of which acknowledge various similarities to classical Arianism.
A letter from Arius to the Arian Eusebius of Nicomedia succinctly states the core beliefs of the Arians:
In 321, Arius was denounced by a synod at Alexandria for teaching a heterodox view of the relationship of Jesus to God the Father. Because Arius and his followers had great influence in the schools of Alexandria—counterparts to modern universities or seminaries—their theological views spread, especially in the eastern Mediterranean.
By 325, the controversy had become significant enough that the Emperor Constantine called an assembly of bishops, the First Council of Nicaea, which condemned Arius' doctrine and formulated the Original Nicene Creed, forms of which are still recited in Catholic, Orthodox, Anglican, and some Protestant services. The Nicene Creed's central term, used to describe the relationship between the Father and the Son, is Homoousios, or Consubstantiality, meaning "of the same substance" or "of one being". (The Athanasian Creed is less often used but is a more overtly anti-Arian statement on the Trinity.)
The focus of the Council of Nicaea was the divinity of Christ (see Paul of Samosata and the Synods of Antioch). Arius taught that Jesus Christ was divine and was sent to earth for the salvation of mankind but that Jesus Christ was not equal to the Father (infinite, primordial origin) and to the Holy Spirit (giver of life). Under Arianism, Christ was instead not consubstantial with God the Father. Since both the Father and the Son under Arius were made of "like" essence or being (see homoiousia) but not of the same essence or being (see homoousia). Ousia is essence or being, in Eastern Christianity, and is the aspect of God that is completely incomprehensible to mankind and human perception. It is all that subsists by itself and which has not its being in another. God the Father and God the Son and God the Holy Spirit all being uncreated. According to the teaching of Arius, the preexistent Logos and thus the incarnate Jesus Christ was a created being, of a distinct, though similar, essence or substance to the Creator; his opponents argued that this would make Jesus less than God, and that this was heretical. Much of the distinction between the differing factions was over the phrasing that Christ expressed in the New Testament to express submission to God the Father. The theological term for this submission is kenosis. This Ecumenical council declared that Jesus Christ was a distinct being of God in existence or reality (hypostasis), which the Latin fathers translated as persona. Jesus was God in essence, being and or nature (ousia), which the Latin fathers translated as substantia.
Constantine exiled those who refused to accept the Nicean creed—Arius himself, the deacon Euzoios, and the Libyan bishops Theonas of Marmarica and Secundus of Ptolemais—and also the bishops who signed the creed but refused to join in condemnation of Arius, Eusebius of Nicomedia and Theognis of Nicaea. The Emperor also ordered all copies of the Thalia, the book in which Arius had expressed his teachings, to be burned.
Although he was committed to maintaining what the church had defined at Nicaea, Constantine was also bent on pacifying the situation and eventually became more lenient toward those condemned and exiled at the council. First he allowed Eusebius of Nicomedia, who was a protégé of his sister, and Theognis to return once they had signed an ambiguous statement of faith. The two, and other friends of Arius, worked for Arius' rehabilitation. At the First Synod of Tyre in AD 335, they brought accusations against Athanasius, bishop of Alexandria, the primary opponent of Arius; after this, Constantine had Athanasius banished, since he considered him an impediment to reconciliation. In the same year, the Synod of Jerusalem under Constantine's direction readmitted Arius to communion in AD 336. Arius, however, died on the way to this event in Constantinople. Several scholarly studies suggest that Arius was poisoned by his opponents. Eusebius and Theognis remained in the Emperor's favour, and when Constantine, who had been a catechumen much of his adult life, accepted baptism on his deathbed, it was from Eusebius of Nicomedia.
Hence, after Constantine's death in 337, open dispute resumed again. Constantine's son Constantius II, who had become Emperor of the eastern part of the Empire, actually encouraged the Arians and set out to reverse the Nicene creed. His advisor in these affairs was Eusebius of Nicomedia, who had already at the Council of Nicea been the head of the Arian party, who also was made bishop of Constantinople.
Constantius used his power to exile bishops adhering to the Nicene creed, especially Athanasius of Alexandria, who fled to Rome. In 355 Constantius became the sole Emperor and extended his pro-Arian policy toward the western provinces, frequently using force to push through his creed, even exiling Pope Liberius and installing Antipope Felix II.
As debates raged in an attempt to come up with a new formula, three camps evolved among the opponents of the Nicene creed. The first group mainly opposed the Nicene terminology and preferred the term homoiousios (alike in substance) to the Nicene homoousios, while they rejected Arius and his teaching and accepted the equality and coeternality of the persons of the Trinity. Because of this centrist position, and despite their rejection of Arius, they were called "semi-Arians" by their opponents. The second group also avoided invoking the name of Arius, but in large part followed Arius' teachings and, in another attempted compromise wording, described the Son as being like (homoios) the Father. A third group explicitly called upon Arius and described the Son as unlike (anhomoios) the Father. Constantius wavered in his support between the first and the second party, while harshly persecuting the third.
The debates between these groups resulted in numerous synods, among them the Council of Sardica in 343, the Council of Sirmium in 358 and the double Council of Rimini and Seleucia in 359, and no less than fourteen further creed formulas between 340 and 360, leading the pagan observer Ammianus Marcellinus to comment sarcastically: "The highways were covered with galloping bishops." None of these attempts was acceptable to the defenders of Nicene orthodoxy: writing about the latter councils, Saint Jerome remarked that the world "awoke with a groan to find itself Arian."
After Constantius' death in 361, his successor Julian, a devotee of Rome's pagan gods, declared that he would no longer attempt to favor one church faction over another, and allowed all exiled bishops to return; this had the objective of further increasing dissension among Christians. The Emperor Valens, however, revived Constantius' policy and supported the "Homoian" party, exiling bishops and often using force. During this persecution many bishops were exiled to the other ends of the Empire, (e.g., Hilarius of Poitiers to the Eastern provinces). These contacts and the common plight subsequently led to a rapprochement between the Western supporters of the Nicene creed and the homoousios and the Eastern semi-Arians.
Two days after Theodosius arrived in Constantinople, November 24, 380, he expelled the Homoian bishop, Demophilus of Constantinople, and surrendered the churches of that city to Gregory Nazianzus, the leader of the rather small Nicene community there, an act which provoked rioting. Theodosius had just been baptized, by bishop Acholius of Thessalonica, during a severe illness, as was common in the early Christian world. In February he and Gratian published an edict that all their subjects should profess the faith of the bishops of Rome and Alexandria (i.e., the Nicene faith), or be handed over for punishment for not doing so.
Although much of the church hierarchy in the East had opposed the Nicene creed in the decades leading up to Theodosius' accession, he managed to achieve unity on the basis of the Nicene creed. In 381, at the Second Ecumenical Council in Constantinople, a group of mainly Eastern bishops assembled and accepted the Nicene Creed of 381, which was supplemented in regard to the Holy Spirit, as well as some other changes, see Comparison between Creed of 325 and Creed of 381. This is generally considered the end of the dispute about the Trinity and the end of Arianism among the Roman, non-Germanic peoples.
The conflict in the 4th century had seen Arian and Nicene factions struggling for control of the Church. In contrast, in the Arian German kingdoms established on the wreckage of the Western Roman Empire in the 5th century, there were entirely separate Arian and Nicene Churches with parallel hierarchies, each serving different sets of believers. The Germanic elites were Arians, and the majority population Nicene. Many scholars see the persistence of the Germanic Arianism as a strategy to differentiate the Germanic elite from the local inhabitants and culture and to maintain their group identity.
Most Germanic tribes were generally tolerant of the Nicene beliefs of their subjects. However, the Vandals tried for several decades to force their Arian belief on their North African Nicene subjects, exiling Nicene clergy, dissolving monasteries, and exercising heavy pressure on non-conforming Christians.
By the beginning of the 8th century, these kingdoms had either been conquered by Nicene neighbors (Ostrogoths, Vandals, Burgundians) or their rulers had accepted Nicene Christianity (Visigoths, Lombards).
Archbishop Dmitri of the Orthodox Church in America said Islam is the largest descendant of Arianism today. There is some superficial similarity in Islam's teaching that Jesus was a great prophet, but very distinct from God, although Islam sees Jesus as a human messenger of God without the divine properties that Arianism attributes to Christ. Islam sees itself as a continuation of the Jewish and Christian traditions and reveres many of the same prophets.
Thus, over the past 1,500 years, some Christians have used the term Arian to refer to those groups that see themselves as worshiping Jesus Christ or respecting his teachings, but do not hold to the Nicene creed. Despite the frequency with which this name is used as a polemical label, there has been no historically continuous survival of Arianism into the modern era.
There have been religious movements holding beliefs that either they, or their opponents, have considered Arian. To quote the Encyclopaedia Britannica's article on Arianism: "In modern times some Unitarians are virtually Arians in that they are unwilling either to reduce Christ to a mere human being or to attribute to him a divine nature identical with that of the Father. However, their doctrines cannot be considered representative of traditional Arian doctrines or vice-versa.