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Monophysitism (// or //) or monophysism (//) (from Greek μόνος monos, "solitary" and φύσις physis, "nature") is a Christology that states that the person of the incarnated Word (that is, in Jesus Christ) there was only one nature—the divine".
The First Council of Nicaea (325) declared that Christ was divine (homoousios, consubstantial, of one being or essence, with the Father) and human (was incarnate and became man). In the fifth century a heated controversy arose between the sees and theological schools of Antioch and Alexandria about how divinity and humanity existed in Christ, the former stressing the humanity, the latter the divinity of Christ. Cyril of Alexandria succeeded in having Nestorius, a prominent exponent of the Antiochian school, condemned at the Council of Ephesus in 431, and insisted on the formula "one physis of the incarnate Word", claiming that any formula that spoke of two physeis represented Nestorianism. Some taught that in Christ the human nature was completely absorbed by the divine, leaving only a divine nature. In 451, the Council of Chalcedon, on the basis of Pope Leo the Great's 449 declaration, defined that in Christ there were two natures united in one person.
Those who insisted on the "one physis" formula, Miaphysites, were referred to as Monophysites, while those who accepted the "two natures" definition were called Dyophysites, a term applied also to followers of Nestorianism.
The forms of monophysism were numerous, and included the following:
Concerning verbal declarations of Monophysitism, Justo L. González stated, "in order not to give an erroneous idea of the theology of the so-called Monophysite churches, that have subsisted until the twentieth century, one should point out that all the extreme sects of Monophysism disappeared within a brief span, and that the Christology of the present so-called Monophysite churches is closer to a verbal than to a real Monophysism". 
Under Emperor Basiliscus, who ousted Emperor Zeno in 475, "the Monophysites reached the pinnacle of their power". In his Encyclion, which he issued in the same year, he revoked the Council of Chalcedon and recognized the Second Council of Ephesus of 449 except for its approval of Eutyches, whom Basiliscus condemned. He required his edict to be signed by each bishop. Among the signatures he obtained were those of three of the four Eastern Patriarchs, but the Patriarch and the populace of the capital protested so resolutely that in 476, seeing that his overthrow was imminent, he issued his Anti-Encyclion revoking his former edict. In the same year, Zeno returned victoriously.
Events had made it clear that there was a split between the population, staunchly Chalcedonian in sympathies, of Constantinople and the Balkans and the largely anti-Chalcedonian population of Egypt and Syria. In an attempt to reconcile both sides, Zeno, with the support of Acacius of Constantinople and Peter III of Alexandria, tried to enforce the compromise Henoticon (Formula of Union) decree of 482, which condemned Eutyches but ignored Chalcedon. Schisms followed on both sides. Rome excommunicated Acacius (leading to the 35-year Acacian schism), while in Egypt the Acephali broke away from Peter III. The Acacian schism continued under Zeno's successor, the Monophysite Anastasius I Dicorus and ended only with the accession of the Chalcedonian Justin I in 518.
Justin I was succeeded by the Chalcedonian Justinian I (527–565), whose wife, however, the Empress Theodora, protected and assisted the Monophysites. Ghassanid patronage of the Monophysite Syrian Church during this time, under phylarch Al-Harith ibn Jabalah, was crucial for its survival and revival, and even its spread. Justinian I was followed by Justin II, who, after being, perhaps because of Theodora's influence, a Monophysite, converted to the Chalcedonian faith before obtaining the imperial throne. Some time later, he adopted a policy of persecuting the Monophysites. From Justinian I on, no emperor was a declared Monophysite, although they continued their efforts to find compromise formulas such as monoenergism and monothelitism.