The Arian controversy was a series of Christian disputes about the nature of Christ that began with a dispute between Arius and Athanasius of Alexandria, two Christian theologians from Alexandria, Egypt. The most important of these controversies concerned the relationship between the substance of God the Father and the substance of His Son.
Emperor Constantine, through the Council of Nicaea in 325, attempted to unite Christianity and establish a single, imperially approved version of the faith. Ironically, his efforts were the cause of the deep divisions created by the disputes after Nicaea.
These disagreements divided the Church into various factions for over 55 years, from the time before the First Council of Nicaea in 325 until after the First Council of Constantinople in 381. There was no formal schism.
Inside the Roman Empire, the Trinitarian faction ultimately gained the upper hand through the Edict of Thessalonica, issued on 27 February AD 380, which made Nicene Christology the state religion of the Roman Empire, and through strict enforcement of that edict. However, outside the Roman Empire, Arianism and other forms of Unitarianism continued to be preached for some time (without the blessing of the Empire), but it was eventually killed off. The modern Roman Catholic Church and the Eastern Orthodox Church, as well as most other modern Christian sects, have generally followed the Trinitarian formulation, though each has its own specific theology on the matter.
The early history of the controversy must be pieced together from about 35 documents found in various sources. The Trinitarian historian Socrates of Constantinople reports that Arius first became controversial under the bishop Alexander of Alexandria, when Arius formulated the following syllogism:
"If the Father begat the Son, he that was begotten had a beginning of existence: hence it is that there was when the Son was not. It follows then of necessity that he had his existence from the non-existence".
Bishop Alexander of Alexandria was criticised for his slow reaction against Arius. Like his predecessor, Dionysius, he has been charged with vacillation. According to Eusebius's work, The Life of Constantine, the controversy had spread from Alexandria into almost all the African regions, and was considered a disturbance of the public order by the Roman Empire. Constantine the Great (Constantine I) sent two letters to Arius and Bishop Alexander, asking the religious leaders to stop the controversy. The ongoing controversy led to Constantine's oversight of the First Council of Nicaea.
Arianism would not be contained within the Alexandrian diocese. By the time Bishop Alexander finally acted against his presbyter, Arius's doctrine had spread far beyond his own see; it had become a topic of discussion—and disturbance—for the entire Church.
The Church was now a powerful force in the Roman world, with Constantine I having legalized it in 313 through the Edict of Milan. "Constantine desired that the church should contribute to the social and moral strength of the empire, religious dissension was a menace to the public welfare." Consequently, the emperor had taken a personal interest in several ecumenical issues, including the Donatist controversy in 316. He also wanted to bring an end to the Arian dispute.
To this end, the emperor sent bishop Hosius of Corduba to investigate and, if possible, resolve the controversy. Hosius was armed with an open letter from the Emperor: "Wherefore let each one of you, showing consideration for the other, listen to the impartial exhortation of your fellow-servant." As the debate continued to rage despite Hosius' efforts, Constantine in AD 325 took an unprecedented step: he called an ecumenical council at Nicaea composed of church prelates from all parts of the empire to resolve this issue, possibly at Hosius' recommendation. It is traditionally said that 318 bishops came to Nicaea to attend the council, though others suggest figures from 250-300. The vast majority of those bishops were from the East. Italy, Spain, Gaul, North Africa, Persia, and Scythia each sent one bishop.
Pope Sylvester I, himself too aged to attend, sent two priests as his delegates. Arius himself attended the council as well as the young deacon Athanasius, who attended as an assistant to Alexander of Alexandria and who would become the champion of the Nicene Creed and spend most of his life battling Arianism and other form of Unitarianism. Also there were Eusebius of Caesarea and Eusebius of Nicomedia. Before the main conclave convened, Hosius initially met with Alexander and his supporters at Nicomedia. The council was presided over by the emperor himself, who participated in and even led some of its discussions.
Those who upheld the notion that Christ was co-eternal and con-substantial with the Father were led by the young archdeacon Athanasius. Those who instead insisted that the Son of God came after God the Father in time and substance, were led by Arius the presbyter. For about two months, the two sides argued and debated, with each appealing to Scripture to justify their respective positions. Arius maintained that the Son of God was a Creature, made from nothing; and that he was God's First Production, before all ages. And he argued that everything else was created through the Son. Thus, said Arius, only the Son was directly created and begotten of God; furthermore, there was a time that He had no existence. He was capable of His own free will, said Arius, and thus "were He in the truest sense a son, He must have come after the Father, therefore the time obviously was when He was not, and hence He was a finite being."
According to some accounts in the hagiography of Saint Nicholas, debate at the council became so heated that at one point, he slapped Arius in the face. The majority of the bishops at the council ultimately agreed upon a creed, known thereafter as the Nicene Creed formulated at the first council of Nicaea. It included the word homoousios, meaning "consubstantial", or "same in essence", which was incompatible with Arius' beliefs. On June 19, 325, council and emperor issued a circular to the churches in and around Alexandria: Arius and two of his unyielding partisans (Theonas and Secundus) were deposed and exiled to Illyricum, while three other supporters—Theognis of Nicaea, Eusebius of Nicomedia and Maris of Chalcedon—affixed their signatures solely out of deference to the emperor. However, Constantine soon found reason to suspect the sincerity of these three, for he later included them in the sentence pronounced on Arius.
In 358, the emperor Constantius II requested two councils, one of the western bishops at Ariminum (now Rimini in Northern Italy) and one of the eastern bishops at Nicomedia.
In 359, the western council met at Ariminum. Ursacius of Singidunum and Valens of Mursa, following the new creed drafted at Sirmium (359), proposed that, "according to the scriptures," the Son was "like the Father." This is known as the Homoian view which held that the Bible does not reveal whether the Son is of the same substance as the Father and we, therefore, should not speculate about such things. This view is in opposition to the "of the same substance" (Homoousios) view of the Nicene Creed. The council, including some supporters of the older creed, accepted this proposal. After the council, Pope Liberius condemned the creed of Ariminum, while his rival, Pope Felix II, supported it.
An earthquake struck Nicomedia, and in 359 the eastern council met at Seleucia Isauria instead. The council was bitterly divided and procedurally irregular, and the two parties met separately and reached opposing decisions. Following the Homoian view, Acacius of Caesarea declared that the Son was "like the Father". But Basil of Ancyra and his party, following a (Homoiousian) Creed of Antioch from 341, declared that the Son was of "similar substance" to the Father. The majority at Seleucia accepted the "similar substance" view and deposed the opposing party.
Constantius did not accept this outcome and requested a third council, at Constantinople (359), of both the eastern and western bishops, to resolve the split at Seleucia. Acacius and Basil of Ancyra, respectively, again proposed the "like the Father" and "similar substance" views, as were explained at Seleucia. However, Maris of Chalcedon, Eudoxius of Antioch, and the deacons Aëtius of Antioch and Eunomius of Cyzicus proposed a third view which was similar to Arius' teachings, namely that the Son was of "a dissimilar substance" from the Father. The Heteroousians ("dissimilar substance") won the victory over the other two views in an initial debate. However, Constantius was not willing to accept this outcome either. He intervened and banished Aëtius; one of the leading proponents of the "dissimilar substance" view. After this, the council, including Maris and Eudoxius, agreed to a fourth view, namely the homoian ("like the Father") view that was already agreed to at Ariminum. They made only minor modifications to the Ariminum creed.
After the Council of Constantinople, the homoian bishop Acacius deposed and banished several homoiousian bishops, including Macedonius I of Constantinople, Basil, Eustathius, Eleusius of Cyzicus, Dracontius of Pergamum, Neonas of Seleucia, Sophronius of Pompeiopolis, Elpidius of Satala and Cyril of Jerusalem. At the same time, Acacius also deposed and banished the Anomoean deacon Aëtius.
In 360, Acacius appointed Eudoxius of Antioch to replace Macedonius and Athanasius of Ancyra to replace Basil, as well as Onesimus of Nicomedia to replace Cecropius, who had died in the earthquake at Nicomedia.
In 361, Constantius died and Julian became sole Roman emperor. Julian demanded the restoration of several pagan temples which Christians had seized or destroyed. According to Philostorgius, pagans killed George of Laodicea, bishop of Alexandria, allowing Athanasius to reclaim the 'see', or ecclesiastical jurisdiction.
The Homoousians taught that the Son is of the same substance as the Father, i.e. both uncreated. The Sabellian form had been condemned as heresy in the 3rd century by Pope Calixtus. The Athanasian form would be declared orthodox at the Council of Constantinople in 383, and has become the basis of most of modern trinitarianism.
According to the historian Socrates of Constantinople, Marcellus of Ancyra and Photinus taught "that Christ was a mere man." Their opponents associated the teachings of Marcellus of Ancyra and Photinus of Sirmium with those of Sabellius and Paul of Samosata, which had been widely rejected before the controversy.
The Homoiousian school taught that the Son is of a similar substance to the Father but not the same.
The Homoians taught that the Son is similar to the Father, either "in all things" or "according to the scriptures," without speaking of substance. Several members of the other schools, such as Hosius of Cordoba and Aëtius, also accepted certain Homoian formulae.
The Heteroousians taught that the Son is of a different substance from the Father, i.e. created. Arius had taught this early in the controversy, and Aëtius would teach the later Anomoean form.
Many critics of the "Nicene" Creed cannot be clearly associated with one school, often due to lack of sources, or due to contradictions between sources.
General info from Wikipedia.org