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Nestorianism is a term used in Christian theology and Church history to refer to several mutually related but doctrinarily distinct sets of teachings.  The first meaning of the term is related to the original teachings of Christian theologian Nestorius (d.c. 450 AD), who promoted specific doctrines in the fields of Christology and Mariology. The second meaning of the term is much wider, and relates to a set of later theological teachings, that were traditionally labeled as Nestorian, but differ from the teachings of Nestorius in origin, scope and terminology.  The Oxford English Dictionary defines Nestorianism as "The doctrine of Nestorius, patriarch of Constantinople (appointed in 428), by which Christ is asserted to have had distinct human and divine persons." 
Original Nestorianism is attested primarily by works of Nestorius, and also by other theological and historical sources that are related to his teachings in the fields of Mariology and Christology. His theology was influenced by teachings of Theodore of Mopsuestia (d. 428), the most prominent theologian of the Antiochian School. Nestorian Mariology rejects the title Theotokos ('God-bearer') for Mary, thus emphasizing distinction between divine and human aspects of the Incarnation. Nestorian Christology promotes the concept of a prosopic union of two natures (divine and human) in Jesus Christ,  thus trying to avoid and replace the concept of a hypostatic union. This Christological position is defined as radical dyophysitism,  and differs from orthodox dyophysitism, that was reaffirmed at the Council of Chalcedon (451).  Such teachings brought Nestorius into conflict with other prominent church leaders, most notably Cyril of Alexandria, who issued 12 anathemas against him (430). Nestorius and his teachings were eventually condemned as heretical at the Council of Ephesus in 431, and again at the Council of Chalcedon in 451. His teachings were considered as heretical not only in Chalcedonian Christianity, but even more in Oriental Orthodoxy. 
After the condemnation, some supporters of Nestorius, who were followers of the Antiochian School and the School of Edessa, relocated to the Sasanian Empire, where they were affiliated with the local Christian community, known as the Church of the East. During the period from 484 to 612, gradual development led to the creation of specific doctrinal views within the Church of the East.  Evolution of those views was finalized by prominent East Syriac theologian Babai the Great (d. 628) who was using the specific Syriac term qnoma (ܩܢܘܡܐ) as a designation for dual (divine and human) substances within one prosopon (person or hypostasis) of Christ. Such views were officially adopted by the Church of the East at a council held in 612.  Opponents of such views labeled them as "Nestorian" thus creating the practice of misnaming the Church of the East as Nestorian.  For a long time, such labeling seemed appropriate, since Nestorius is officially venerated as a saint in the Church of the East.  In modern religious studies, this label has been criticized as improper and misleading.  As a consequence, the use of Nestorian label in scholarly literature, and also in the field of inter-denominational relations, is gradually being reduced to its primary meaning, focused on the original teachings of Nestorius. 
Nestorianism was condemned as heresy at the Council of Ephesus (431). The Armenian Church rejected the Council of Chalcedon (451) because they believed Chalcedonian Definition was too similar to Nestorianism. The Persian Nestorian Church, on the other hand, supported the spread of Nestorianism in Persarmenia. The Armenian Church and other eastern churches saw the rise of Nestorianism as a threat to the independence of their Church. Peter the Iberian, a Georgian prince, also strongly opposed the Chalcedonian Creed.  Thus, in 491, Catholicos Babken I of Armenia, along with the Albanian and Iberian bishops met in Vagharshapat and issued a condemnation of the Chalcedonian Definition. 
Nestorians held that the Council of Chalcedon proved the orthodoxy of their faith and had started persecuting non-Chalcedonian or Miaphysite Syriac Christians during the reign of Peroz I. In response to pleas for assistance from the Syriac Church, Armenian prelates issued a letter addressed to Persian Christians reaffirming their condemnation of the Nestorianism as heresy. 
Following the exodus to Persia, scholars expanded on the teachings of Nestorius and his mentors, particularly after the relocation of the School of Edessa to the (then) Persian city of Nisibis (modern-day Nusaybin in Turkey) in 489, where it became known as the School of Nisibis.[ citation needed ] Nestorian monasteries propagating the teachings of the Nisibis school flourished in 6th century Persarmenia. 
Despite this initial Eastern expansion, the Nestorians' missionary success was eventually deterred. David J. Bosch observes, "By the end of the fourteenth century, however, the Nestorian and other churches—which at one time had dotted the landscape of all of Central and even parts of East Asia—were all but wiped out. Isolated pockets of Christianity survived only in India. The religious victors on the vast Central Asian mission field of the Nestorians were Islam and Buddhism". 
Nestorianism is a radical form of dyophysitism,  differing from orthodox dyophysitism on several points, mainly by opposition to the concept of hypostatic union. It can be seen as the antithesis to Eutychian Monophysitism, which emerged in reaction to Nestorianism. Where Nestorianism holds that Christ had two loosely united natures, divine and human, Monophysitism holds that he had but a single nature, his human nature being absorbed into his divinity. A brief definition of Nestorian Christology can be given as: "Jesus Christ, who is not identical with the Son but personally united with the Son, who lives in him, is one hypostasis and one nature: human."  This contrasts with Nestorius' own teaching that the Word, which is eternal, and the Flesh, which is not, came together in a hypostatic union, 'Jesus Christ', Jesus thus being both fully man and God, of two ousia (Ancient Greek : οὐσία ) (essences) but of one prosopon (person).  Both Nestorianism and Monophysitism were condemned as heretical at the Council of Chalcedon.
Nestorius developed his Christological views as an attempt to understand and explain rationally the incarnation of the divine Logos, the Second Person of the Holy Trinity as the man Jesus. He had studied at the School of Antioch where his mentor had been Theodore of Mopsuestia; Theodore and other Antioch theologians had long taught a literalist interpretation of the Bible and stressed the distinctiveness of the human and divine natures of Jesus. Nestorius took his Antiochene leanings with him when he was appointed Patriarch of Constantinople by Byzantine emperor Theodosius II in 428.
Nestorius's teachings became the root of controversy when he publicly challenged the long-used title Theotokos  ('God-Bearer') for Mary. He suggested that the title denied Christ's full humanity, arguing instead that Jesus had two persons (dyoprosopism),  the divine Logos and the human Jesus. As a result of this prosopic duality, he proposed Christotokos ('Christ-Bearer') as a more suitable title for Mary. He also advanced the image of Jesus as a warrior-king and rescuer of Israel over the traditional image of the Christus dolens . 
Nestorius' opponents found his teaching too close to the heresy of adoptionism – the idea that Christ had been born a man who had later been "adopted" as God's son. Nestorius was especially criticized by Cyril, Patriarch of Alexandria, who argued that Nestorius's teachings undermined the unity of Christ's divine and human natures at the Incarnation. Some of Nestorius's opponents argued that he put too much emphasis on the human nature of Christ, and others debated that the difference that Nestorius implied between the human nature and the divine nature created a fracture in the singularity of Christ, thus creating two Christ figures.  Nestorius himself always insisted that his views were orthodox, though they were deemed heretical at the Council of Ephesus in 431, leading to the Nestorian Schism, when churches supportive of Nestorius and the rest of the Christian Church separated. However, this formulation was never adopted by all churches termed 'Nestorian'. Indeed, the modern Assyrian Church of the East, which reveres Nestorius, does not fully subscribe to Nestorian doctrine, though it does not employ the title Theotokos. 
Nestorianism became a distinct sect following the Nestorian Schism, beginning in the 430s. Nestorius had come under fire from Western theologians, most notably Cyril of Alexandria. Cyril had both theological and political reasons for attacking Nestorius; on top of feeling that Nestorianism was an error against true belief, he also wanted to denigrate the head of a competing patriarchate.[ citation needed ] Cyril and Nestorius asked Pope Celestine I to weigh in on the matter. Celestine found that the title Theotokos  was orthodox, and authorized Cyril to ask Nestorius to recant. Cyril, however, used the opportunity to further attack Nestorius, who pleaded with Emperor Theodosius II to call a council so that all grievances could be aired. 
In 431 Theodosius called the Council of Ephesus. However, the council ultimately sided with Cyril, who held that the Christ contained two natures in one divine person (hypostasis, unity of subsistence), and that the Virgin Mary, conceiving and bearing this divine person, is truly called the Mother of God (Theotokos). The council accused Nestorius of heresy, and deposed him as patriarch.  Upon returning to his monastery in 436, he was banished to Upper Egypt. Nestorianism was officially anathematized, a ruling reiterated at the Council of Chalcedon in 451. However, a number of churches, particularly those associated with the School of Edessa, supported Nestorius – though not necessarily his doctrine – and broke with the churches of the West. Many of Nestorius' supporters relocated to the Sasanian Empire of Iran, home to a vibrant but persecuted Christian minority.  In Upper Egypt, Nestorius wrote his Book of Heraclides, responding to the two councils at Ephesus (431, 449). 
The western provinces of the Persian Empire had been home to Christian communities, headed by metropolitans, and later patriarchs of Seleucia-Ctesiphon. The Christian minority in Persia was frequently persecuted by the Zoroastrian majority, which accused local Christians of political leanings towards the Roman Empire. In 424, the Church in Persia declared itself independent, in order to ward off allegations of any foreign allegiance. By the end of the 5th century, the Persian Church increasingly aligned itself with the teachings of Theodore of Mopsuestia and his followers, many of whom became dissidents after the councils of Ephesus (431), and Chalcedon (451). The Persian Church became increasingly opposed to doctrines promoted by those councils, thus furthering the divide between Chalcedonian and Persian currents. 
In 486, the Metropolitan Barsauma of Nisibis publicly accepted Nestorius' mentor Theodore of Mopsuestia as a spiritual authority. In 489, when the School of Edessa in Mesopotamia was closed by Byzantine Emperor Zeno for its pro-Nestorian teachings, the school relocated to its original home of Nisibis, becoming again the School of Nisibis, leading to the migration of a wave of Christian dissidents into Persia. The Persian patriarch Babai (497–502) reiterated and expanded upon the church's esteem for Theodore of Mopsuestia.
Now firmly established in Persia, with centers in Nisibis, Ctesiphon, and Gundeshapur, and several metropoleis, the Persian Church began to branch out beyond the Sasanian Empire. However, through the sixth century, the church was frequently beset with internal strife and persecution by Zoroastrians. The infighting led to a schism, which lasted from 521 until around 539 when the issues were resolved. However, immediately afterward Roman-Persian conflict led to the persecution of the church by the Sassanid emperor Khosrow I; this ended in 545. The church survived these trials under the guidance of Patriarch Aba I, who had converted to Christianity from Zoroastrianism. 
The church emerged stronger after this period of ordeal, and increased missionary efforts farther afield. Missionaries established dioceses in the Arabian Peninsula and India (the Saint Thomas Christians). They made some advances in Egypt, despite the strong miaphysite presence there.  Missionaries entered Central Asia and had significant success converting local Turkic tribes.
The Anuradhapura Cross discovered in Sri Lanka strongly suggests a strong presence of Nestorian Christianity in Sri Lanka during the 6th century AD according to Humphrey Codrington, who based his claim on a 6th-century manuscript, Christian Topography, that mentions of a community of Persian Christians who were known to reside in Taprobanê (the Ancient Greek name for Sri Lanka).   
Nestorian missionaries were firmly established in China during the early part of the Tang dynasty (618–907); the Chinese source known as the Nestorian Stele records a mission under a Persian proselyte named Alopen as introducing Nestorian Christianity to China in 635. The Jingjiao Documents (also described by The Japanese scholar P. Y. Saeki as "Nestorian Documents") or Jesus Sutras are said to be connected with Alopen. 
Following the Arab conquest of Persia, completed in 644, the Persian Church became a dhimmi community under the Rashidun Caliphate. The church and its communities abroad grew larger under the Caliphate. By the 10th century it had 15 metropolitan sees within the Caliphate's territories, and another five elsewhere, including in China and India.  After that time, however, Nestorianism went into decline.[ disputed ]
In a 1996 article published in the Bulletin of the John Rylands Library, Fellow of the British Academy Sebastian Brock wrote: "the term 'Nestorian Church' has become the standard designation for the ancient oriental church which in the past called itself 'The Church of the East', but which today prefers the fuller title 'The Assyrian Church of the East'. The Common Christological Declaration between the Catholic Church and the Assyrian Church of the East signed by Pope John Paul II and Mar Dinkha IV underlines the Chalcedonian Christological formulation as the expression of the common faith of these Churches and recognizes the legitimacy of the title Theotokos." 
In a 2017 paper, Mar Awa Royel, Bishop of the Assyrian Church, stated the position of that church: "After the Council of Ephesus (431), when Nestorius the patriarch of Constantinople was condemned for his views on the unity of the Godhead and the humanity in Christ, the Church of the East was branded as 'Nestorian' on account of its refusal to anathematize the patriarch." 
Several historical records suggest that the Assyrian Church of the East may have been in Sri Lanka between the mid-5th and 6th centuries.   
The Chalcedonian Definition is a declaration of Christ's nature, adopted at the Council of Chalcedon in AD 451. Chalcedon was an early centre of Christianity located in Asia Minor. The council was the fourth of the ecumenical councils that are accepted by Chalcedonian churches which include the Catholic, Eastern Orthodox, Lutheran, Anglican and Reformed churches.
Theotokos is a title of Mary, mother of Jesus, used especially in Eastern Christianity. The usual Latin translations are Dei Genitrix or Deipara. Familiar English translations are "Mother of God" or "God-bearer" – but these both have different literal equivalents in Greek, Μήτηρ Θεοῦ and Θεοφόρος.
The Council of Ephesus was a council of Christian bishops convened in Ephesus in AD 431 by the Roman Emperor Theodosius II. This third ecumenical council, an effort to attain consensus in the church through an assembly representing all of Christendom, confirmed the original Nicene Creed, and condemned the teachings of Nestorius, Patriarch of Constantinople, who held that the Virgin Mary may be called the Christotokos, "Christ-bearer" but not the Theotokos, "God-bearer". It met in June and July 431 at the Church of Mary in Ephesus in Anatolia.
Monophysitism or monophysism is a Christological term derived from the Greek μόνος and φύσις. It is defined as "a doctrine that in the person of the incarnated Word there was only one nature—the divine".
Chalcedonian Christianity is the branch of Christianity that accepts and upholds theological and ecclesiological resolutions of the Council of Chalcedon, the Fourth Ecumenical Council, held in 451. Chalcedonian Christianity accepts the Christological Definition of Chalcedon, a Christian doctrine concerning the union of two natures in one hypostasis of Jesus Christ, who is thus acknowledged as a single person (prosopon). Chalcedonian Christianity also accepts the Chalcedonian confirmation of the Niceno-Constantinopolitan Creed, thus acknowledging the commitment of Chalcedonism to Nicene Christianity.
Nestorius was the Archbishop of Constantinople from 10 April 428 to August 431. A Christian theologian, several of his teachings in the fields of Christology and Mariology were seen as controversial and caused major disputes. He was condemned and deposed from his see by the Council of Ephesus, the third Ecumenical Council, in 431.
Eutyches or Eutyches of Constantinople was a presbyter and archimandrite at Constantinople. He first came to notice in 431 at the First Council of Ephesus, for his vehement opposition to the teachings of Nestorius; his condemnation of Nestorianism as heresy led him to an equally extreme, although opposite view, which precipitated his being denounced as a heretic himself.
The Catechetical School of Antioch was one of the two major centers of the study of biblical exegesis and theology during Late Antiquity; the other was the Catechetical School of Alexandria. This group was known by this name because the advocates of this tradition were based in the city of Antioch, one of the major cities of the ancient Roman Empire.
The Nestorian schism (431) was a split between the Christian churches of Sassanid Persia, which affiliated with Nestorius, and those that later became the Catholic and Orthodox churches. The schism rose out of a Christological dispute, notably involving Cyril and Nestorius.
The School of Nisibis was an educational establishment in Nisibis. It was an important spiritual centre of the early Church of the East, and like the Academy of Gondishapur, it is sometimes referred to as the world's first university. The school had three primary departments teaching: theology, philosophy and medicine. Its most famous teacher was Narsai, formerly head of the School of Edessa.
The Synod of Beth Lapat was a local council of the Church of the East, that was held in 484, in the Persian city of Gundeshapur. The council was headed by Metropolitan Barsauma of Nisibis, who was involved in a long conflict with Patriarch Babowai of Seleucia-Ctesiphon. No acts of this synod have been preserved, but fragmentary data from other sources suggest that various ecclesiological issues had been discussed, and that disciplinary canons against simony were adopted. Since Metropolitan Barsauma was involved in christological disputes, it is believed that several doctrinal questions were also discussed, and some later sources suggest that synod of 484 adopted a resolution in support of theological teachings of Theodore of Mopsuestia. Since no creeds or theological decisions of this council have been preserved, its outcome has been the subject of various assumptions among scholars.
Hypostatic union is a technical term in Christian theology employed in mainstream Christology to describe the union of Christ's humanity and divinity in one hypostasis, or individual existence.
Miaphysitism is the Christological doctrine that holds Jesus, the "Incarnate Word, is fully divine and fully human, in one 'nature' (physis)." It is a position held by the Oriental Orthodox Churches and differs from the Chalcedonian position that Jesus is one "person" in two "natures", a divine nature and a human nature (Dyophysitism).
Eutychianism, also known as Real Monophysitism, refers to a set of Christian theological doctrines derived from the ideas of Eutyches of Constantinople. Eutychianism is a monophysite understanding of how the human and divine relate within the person of Jesus Christ, with Christ being in one nature and of two, with the humanity of Christ subsumed by the divinity.
In Christian theology, dyophysitism is the Christological position that two natures, divine and human, exist in the person of Jesus Christ. It contrasts with monophysitism and miaphysitism.
Coptic history is the part of the history of Egypt that begins with the introduction of Christianity in Egypt in the 1st century AD during the Roman period, and covers the history of the Copts to the present day. Many of the historic items related to Coptic Christianity are on display in many museums around the world and a large number is in the Coptic Museum in Coptic Cairo.
In the history of Christianity, the first seven ecumenical councils include the following: the First Council of Nicaea in 325, the First Council of Constantinople in 381, the Council of Ephesus in 431, the Council of Chalcedon in 451, the Second Council of Constantinople in 553, the Third Council of Constantinople from 680–681 and finally, the Second Council of Nicaea in 787. All of the seven councils were convened in modern-day Turkey.
The Oriental Orthodox Churches are Eastern Christian churches adhering to Miaphysite Christology, with approximately 60 million members worldwide. The Oriental Orthodox Churches are part of the Nicene Christian tradition, and represent one of its oldest branches.
In the 5th century in Christianity, there were many developments which led to further fracturing of the State church of the Roman Empire. Emperor Theodosius II called two synods in Ephesus, one in 431 and one in 449, that addressed the teachings of Patriarch of Constantinople Nestorius and similar teachings. Nestorius had taught that Christ's divine and human nature were distinct persons, and hence Mary was the mother of Christ but not the mother of God. The Council rejected Nestorius' view causing many churches, centered on the School of Edessa, to a Nestorian break with the imperial church. Persecuted within the Roman Empire, many Nestorians fled to Persia and joined the Sassanid Church thereby making it a center of Nestorianism. By the end of the 5th century, the global Christian population was estimated at 10-11 million. In 451 the Council of Chalcedon was held to clarify the issue further. The council ultimately stated that Christ's divine and human nature were separate but both part of a single entity, a viewpoint rejected by many churches who called themselves miaphysites. The resulting schism created a communion of churches, including the Armenian, Syrian, and Egyptian churches, that is today known as Oriental Orthodoxy. In spite of these schisms, however, the imperial church still came to represent the majority of Christians within the Roman Empire.
The Church of the East or the East Syriac Church, also called the Church of Seleucia-Ctesiphon, the Persian Church, the Assyrian Church, the Babylonian Church or the Nestorian Church, was an Eastern Christian church of the East Syriac Rite, based in Mesopotamia. It was one of three major branches of Eastern Christianity that arose from the Christological controversies of the 5th and 6th centuries, alongside the Oriental Orthodox Churches and the Chalcedonian Church. During the early modern period, a series of schisms gave rise to rival patriarchates, sometimes two, sometimes three. Since the latter half of the 20th century, three churches in Iraq claim the heritage of the Church of the East. Meanwhile, the East Syriac churches in India claim the heritage of the Church of the East in India.