Perhaps the best known story about Leo the Great, bishop of Rome from 440 to 461, is his encounter with Attila the Hun in 452. Attila and his army of Huns were marching on Rome. The Roman emperor and senate sought to dissuade him from attacking the city, so they sent an embassy of leading Romans, including Leo, who met Attila and managed to dissuade him from plundering Rome.

This story has acquired legendary accretions that magnify the role of Leo and introduce elements of the supernatural into the story. But what it does convey accurately is the formidable personality of Leo, one of the most imposing of the bishops of Rome. Another of Leo’s exploits was his intervention in the Council of Chalcedon.

Knotty Questions

A central theological issue in the first few centuries was the person of Christ: In what sense was he God? At the beginning of the fourth century Arius claimed that only the Father was truly God. In response, the Council of Nicea proclaimed the full deity of Christ. But if Jesus was truly God, how could he be truly human as well? Indeed, was he? If he was, how can one person be both God and man? Was he, in fact, one person? These and other such questions were to dominate Greek theological debate for the next three-and-a-half centuries.

The Council of Chalcedon (451) comes in the middle—not at the end—of these debates. It marks a significant point at which four crucial issues concerning the person of Christ are clarified:

• against Arius, the full deity of Christ is affirmed

• against Apollinarius, the full humanity of Christ is affirmed

• against Nestorius, it is affirmed that Christ is one person

• against Eutyches, it is affirmed that the deity and humanity of Christ remain distinct and are not blurred together.

Chalcedon was occasioned by the teaching of Eutyches, the last of these four heretics. Eutyches was an elderly monk who was theologically out of his depth rather than willfully heretical. He was condemned at Constantinople (now Istanbul) for denying that Christ is fully like us and for blurring together the two natures of Christ, his humanity and divinity.

Leo’s Tome

Leo wrote a Tome, a theological treatise condemning Eutyches. But the eastern way of settling matters was to convene a general council of bishops. One met in 449, at Ephesus, and took a position different from that of Leo, whose Tome was not read at the council. Eastern leaders of a like mind to Leo were deposed. Leo called this gathering a “robber synod” and tried to have it reversed, without success.

The following year the emperor fell from his horse and died. His successor favored the approach of Leo, and so another council was called, which met at Chalcedon (by Constantinople) in 451. Leo did not attend in person, but he sent delegates. This council reversed the decisions of Ephesus and condemned Eutyches. Leo’s Tome was read and approved, though not without some misgivings. Some bishops wanted to stop there, but the emperor insisted upon a confession of faith to unify the empire. Thus was born the Chalcedonian Definition.

The Definition affirmed that Christ is “truly God,” “perfect in Godhead,” the Son of God who was “begotten of the Father before the ages.” Yet he is also “truly man,” “perfect in manhood” and was born of the Virgin Mary. The deity and humanity are “not parted or divided into two persons,” but Christ is “one person and one being.” Nor are his deity and humanity to be blurred together. “The difference of the [divine and human] natures is in no wise taken away by reason of the union, but rather the properties of each are preserved.” Thus Christ is “made known in two natures [which exist] without confusion, without change, without division, without separation.”

Dynamite-Like Effect

The emperor intended the Definition to unify the empire. Its actual effecet was more like the explosion of dynamite. Large areas of the East would not accept Chalcedon, such as the Coptic churches in Egypt and Ethiopia. The Eastern church was split intotwo, and breakway churches (the “Monophysite,” or “One Nature,” chruches) formed that exist to this day. Various attempts were made to resolve the conflict, which led to further coundcils in 553 and 880/1. But the Eastern emperor, in Constantinople, faced a fundamental dilemma. He could unite the East by dropping Chalcedon, but at the price of losing communion with the West. Alternatively, he could maintain union with the West by holding to Chalcedon, but at the cost of Eastern unity. Ultimately, the conflict ended because the dissenting churches were in areas that came under Muslim control. Today, however, the two sides are moving closer together.

The Chalcedonian Definition has been subjected to considerable criticism in the last two hundred years. The way in which it expresses itself is certainly not perfect. But its condemnation of the four basic heresies is an abiding and valuable contribution.

The Council’s statement remains of considerable relevance since Nestorius’s approach is very much alive in modern liberal christologies that speak of Jesus as a man with a special relationship to God rather than as himself being God incarnate. On the other hand, many who pride themselves on holding a conservative view think of Christ as having a single nature that is either divine (the error of Apollinarius) or a blend of the human and the divine (the error of Eutyches).

Tony Lane is lecturer in historical theology at London Bible College and a member of the advisory board of Christian History