Its story
Eutyches, an elderly archimandrite of a monastery in Constantinople and a fervent opponent of Nestorius, held that Christ was 'of two natures before the union, but of one after', and refused to say that Christ's body was consubstantial with ours. A synod under Patriarch Flavian condemned him in 448. In 449 a synod at Ephesus under Dioscorus of Alexandria restored him and deposed Flavian; Pope Leo, whose letter (the Tome to Flavian) was not read there, called it a latrocinium, the 'Robber Synod of Ephesus'.
The Council of Chalcedon (451) deposed Dioscorus and, receiving Leo's Tome and Cyril's letters, defined that Christ is one and the same, 'acknowledged in two natures, without confusion, without change, without division, without separation', which concur in one person and hypostasis. For many in Egypt and Syria, however, the formula 'in two natures' looked like a concession to Nestorius and a departure from Cyril's formula 'one incarnate nature of the Word'.
From this came the great division that persists today (see the Chalcedon division page). The churches that did not accept Chalcedon—Coptic, Syriac, Armenian, Ethiopian, Eritrean and Malankara—are known today as Oriental Orthodox. They reject the name 'Monophysite', which they associate with Eutyches, whom they also condemn, and describe themselves as miaphysite: they confess in Christ one nature (mia physis) united from divinity and humanity, without mixture, confusion or alteration, following Cyril, Dioscorus and Severus of Antioch. Imperial attempts at reconciliation (the Henotikon of 482, the Second Council of Constantinople in 553) failed to restore communion.
In the 20th century, dialogue produced significant Christological agreements: the common declaration of Pope Paul VI and Coptic Pope Shenouda III (1973); that of Pope John Paul II and Syriac Orthodox Patriarch Ignatius Zakka I (1984); and, with the Eastern Orthodox Church, the agreed statements of Anba Bishoy (1989) and Chambésy (1990), which affirm that both families have kept the same Christological faith in different terminology. These statements have not restored full communion, and some on each side question them; whether the division of 451 was chiefly terminological remains an open question.