The Council of Chalcedon (; Latin: Concilium Chalcedonense) was the fourth ecumenical council of the Christian Church. It was convoked by the Roman emperor Marcian. The council convened in the city of Chalcedon, Bithynia (modern-day Kadıköy, Istanbul, Turkey) from 8 October to 1 November 451. The council was attended by over 520 bishops or their representatives, making it the largest and best-documented of the first seven ecumenical councils. The principal purpose of the council was to re-assert the teachings of the ecumenical Council of Ephesus against the teachings of Eutyches and Nestorius. Such doctrines viewed Christ's divine and human natures as separate and distinct (Nestorianism), or viewed Christ as solely divine (monophysitism). The Council of Chalcedon issued the Chalcedonian Definition, stating that Jesus is "perfect both in deity and in humanness; this selfsame one is also actually God and actually man." The Council's judgments and definitions regarding the divine marked a significant turning point in the Christological debates.
The ruling of the council stated:We all teach harmoniously [that he is] the same perfect in godhead, the same perfect in manhood, truly God and truly man, the same of a reasonable soul and body; homoousios with the Father in godhead, and the same homoousios with us in manhood… acknowledged in two natures without confusion, without change, without division, without separation.
Whilst this judgment marked a significant turning point in the Christological debates, it also generated heated disagreements between the council and the Oriental Orthodox Church, which did not agree with such conduct or proceedings. This disagreement would later cause the Oriental Orthodox Churches and the Chalcedonian churches to schism, and led to the council being regarded as Chalcedon, the Ominous by the Miaphysites.
The council's other responsibilities included addressing controversy, dealing with issues such as ecclesiastical discipline and jurisdiction, and approving statements of belief such as the Creed of Nicaea (325), the Creed of Constantinople (381, subsequently known as the Nicene Creed), two letters of St. Cyril of Alexandria against Nestorius, and the Tome of Pope Leo I. The Christology of the Church of the East may be called "non-Ephesine" for not accepting the Council of Ephesus, but it did finally gather to ratify the Council of Chalcedon at the Synod of Mar Aba I in 544. Through the 1994 Common Christological Declaration between the Chalcedonian Catholic Church and the Nestorian Assyrian Church of the East, the Assyrian Church of the East and the Catholic Church each accepted and confessed the same doctrine of Christology.
In 325, the first ecumenical council (First Council of Nicaea) determined that Jesus Christ was God, "consubstantial" with the Father, and rejected the Arian contention that Jesus was a created being. This was reaffirmed at the First Council of Constantinople (381) and the First Council of Ephesus (431).
About two years after Cyril of Alexandria's death in 444, an aged monk from Constantinople named Eutyches began teaching a subtle variation on the traditional Christology in an attempt to stop what he saw as a new outbreak of Nestorianism. He claimed to be a faithful follower of Cyril's teaching, which was declared orthodox in the Union of 433.
Cyril had taught that "There is only one physis, since it is the Incarnation, of God the Word." It was argued by Pope Leo I that due to potential ambiguity between the various Greek terms and their Latin equivalents, in addition to the energy and imprudence with which he asserted his opinions, Eutyches was misunderstood, and many believed that he was advocating Docetism, a sort of reversal of Arianism – where Arius had denied the consubstantial divinity of Jesus, Eutyches seemed to be denying that Jesus was fully human. Pope Leo I wrote that Eutyches' error seemed to be more from a lack of skill than from malice.
Eutyches had been accusing various personages of covert Nestorianism. In November 448, Flavian, Bishop of Constantinople held a local synod regarding a point of discipline connected with the province of Sardis. At the end of the session of this synod one of those inculpated, Eusebius, Bishop of Dorylaeum, brought a counter charge of heresy against the archimandrite. Eusebius demanded that Eutyches be removed from office. Flavian preferred that the bishop and the archimandrite sort out their differences, but as his suggestion went unheeded, Eutyches was summoned to clarify his position regarding the nature of Christ. Eventually, Eutyches reluctantly appeared, but his position was considered to be theologically unsophisticated, and the synod finding his answers unresponsive condemned and exiled him. Flavian sent a full account to Pope Leo I. Although it had been accidentally delayed, Leo wrote a compendious explanation of the whole doctrine involved, and sent it to Flavian as a formal and authoritative decision of the question.
Eutyches appealed against the decision, labeling Flavian a Nestorian, and received the support of Pope Dioscorus I of Alexandria. John Anthony McGuckin sees an "innate rivalry" between the Sees of Alexandria and Constantinople. Dioscurus, imitating his predecessors in assuming a primacy over Constantinople, held his own synod which annulled the sentence of Flavian, and absolved Eutyches after he claimed to have repented.
Through the influence of the court official Chrysaphius, godson of Eutyches, in 449, the competing claims between the Patriarchs of Constantinople and Alexandria led Emperor Theodosius II to call a council which was held in Ephesus in 449, with Dioscorus presiding.
Pope Leo sent four legates to represent him and expressed his regret that the shortness of the notice must prevent the presence of any other bishop of the West. He provided his legates, one of whom died en route, with a letter addressed to Flavian explaining Rome's position in the controversy. Leo's letter, now known as Leo's Tome, confessed that Christ had two natures, and was not of or from two natures.
On August 8, 449 the Second Council of Ephesus began its first session. The Acts of the first session of this synod were read at the Council of Chalcedon, 451, and are thus preserved. The remainder of the Acts (the first session being wanting) are known through a Syriac translation by a Miaphysite monk, written in the year 535 and published from a manuscript in the British Museum. Nonetheless, there are somewhat different interpretations as to what actually transpired. The question before the council by order of the emperor was whether Flavian, in a synod held by him at Constantinople in November, 448, had justly deposed and excommunicated the Archimandrite Eutyches for refusing to admit two natures in Christ.
Dioscorus began the council by banning all members of the November 448 synod which had deposed Eutyches from sitting as judges. He then introduced Eutyches who publicly professed that while Christ had two natures before the incarnation, the two natures had merged to form a single nature after the incarnation. Of the 130 assembled bishops, 111 voted to rehabilitate Eutyches.
Throughout these proceedings, Hilary (one of the papal legates) repeatedly called for the reading of Leo's Tome, but was ignored. The Eastern Orthodox Church has very different accounts of The Second Council of Ephesus. Pope Dioscorus requested deferring reading of Leo's Tome, as it was not seen as necessary to start with, and could be read later. This was seen as a rebuke to the representatives from the Church of Rome not reading the Tome from the start.
Not having wanted for the letter to be read aloud for this reason, Dioscorus was then forced to depose Flavian of Constantinople and Eusebius of Dorylaeum on the grounds that they taught the Word having two distinct hypostases, in contrast to Cyril's teachings. According to Chalcedonian accounts, when Flavian and Hilary objected, Dioscorus called for a mob to enter the church which assaulted Flavian as he clung to the altar; other accounts blame one monk, Barsauma, and others yet blame Dioscorus himself. Flavian would die three days later. Other sources, however, implicate Empress Pulcheria and Anatolius of Constantinople, as it would not be realistic for a murder witnessed by many bishops and patriarchs at a major council to go unmentioned, and Flavian himself has letters to Leo after the council that make no mention of such events.