The doctrine of the Trinity is one of the fundamental teachings of Christianity, upheld by almost every denomination in the world. It is unquestioned largely because its meaning and relevance are obscure to almost every modern Christian. However, between 300 and 600 AD, battles over the Trinity consumed both theologians and ordinary people throughout Europe, the Middle East, and North Africa.

History of the Trinity 1: Until 325

The doctrine of the Trinity was developed to explain the relationship between God, Jesus, and the Holy Spirit. All three of these beings are described in the Bible, and it's clear that they were part of Christianity even before the Bible was written in the late 1st century. The Bible says a variety of things about Jesus and the Holy Spirit. Some Biblical texts make it seem as though Jesus is God (see especially John 1). Other texts indicate that there are differences between Jesus and God. Beyond the question of Biblical text, there's the fact that Jesus lived a completely human life, even to the point of death--since God is immortal, how can it be said that Jesus is God? This is only one of a number of rather obvious questions that the Trinity is supposed to address.

In the earliest period of Christianity, these questions didn't trouble Christians too much. They knew that their experiences of Jesus and the Holy Spirit were experiences of God. But in the 2nd and 3rd centuries, as Christianity expanded in the Roman Empire and elsewhere, many Christians attempted to explain their faith in the categories of Hellenistic philosophy that were familiar to them and the people they wanted to convert. Middle Platonism, the philosophy current at the time, envisioned a hierarchy of beings that began with the ultimate being and led downward, through a chain of mediating spiritual beings, to the physical world. With this philosophy, it was obvious that Jesus and the Spirit were the first and second divine mediators between God and the world. However, there was another school that pursued a very different line of thought. They saw Jesus as the union between the divine and the human--as the presence of God in the world and in the human soul. Jesus, the word made flesh, bridged the gap between human and God, between infinite and finite--and made it possible for all humans to experience theosis or divinization. If Jesus was not fully God as well as fully human, then humans were still separated from God and not saved. These people insisted on saying that Jesus was truly God.

Between 250 and 320 there were a whole variety of formulations that attempted to express all these complexities. As these formulations became increasingly refined, the people who held them became increasingly hostile toward each other, and matters came to a head in 321 when Arius, a popular presbyter from Alexandria who held that Jesus was divine but not God, was excommunicated by a council of bishops from the area. Arius refused to recant, and instead travelled to Syria to continue teaching his ideas.

Shortly after this, Constantine, the Roman Emperor, legalized Christianity and moved to make it a state religion. For him, the vicious internal battle between the Arians and their opponents was a destabilizing force that could not be tolerated. Therefore, he ordered the Christian bishops to meet and work out their differences.

History of the Trinity 2: 325-600

In 325, to resolve the theological battles over the nature of the Trinity that were dividing Christianity--and, as a consequence, the Roman Empire--Emperor Constantine called together the Christian bishops to discuss the matter and come to some sort of agreement. The Council met at Nicaea, a town outside the new capital of Constantinople. On one side, the Arians held that Jesus, while divine, was a created being who was inferior to God. The other group believed that Jesus, though in a human body, was also God.

The anti-Arians came up with the Greek word "homoousios" (translated as "one in being" or "of the same being") to describe the relationship between Jesus and "the Father," the unapproachable God that Jesus talked about. They said that while Jesus and the Father could be distinguished, they shared one being or nature. The Arians pointed out that this position created a lot of complicated questions, and that the word "homoousios" never appeared in the Bible. Despite this, the First Council of Nicaea adopted the anti-Arian position and excommunicated Arius.

This was not the end of the story. The next decades saw a long and complicated struggle between the Arian and anti-Arian communities across the Roman Empire. The religious turmoil was exacerbated by the frequent overthrow of emperors, as each new ruler took a different position on the question. Despite dozens of councils and mutual excommunications, the conflict continued on for decades. It is important to realize that these conflicts were not matters only for theologians and specialists--St. Basil, the patriarch of Constaninople, complained that when he tried to get bread from the bakery, the baker tried to convince him that the Father was greater than the Son. Ordinary people as well as professionals were caught up in the dispute.

Within the Empire, the Arians were finally forced out during the reign of Theodosius, a strong and firmly anti-Arian Emperor. The First Council of Constantinople, held in 381, broadly affirmed the use of "homoousios" and also affirmed that the Holy Spirit, like Jesus, was distinct but of the same being as the Father. Thus, the traditional formula (translated into English as "three persons with one nature") was in place.

This was not completely the end of the story. Arian missionaries preached to barbarian tribes and converted several--notably the Lombards, Vandals, and Visigoths--to Arian Christianity. When these groups conquered Roman provinces they maintained their religion, although all eventually converted to non-Arian Christianity over time. The Visigothic king of Spain, the last major Arian ruler, renounced Arianism in the mid-6th century. Within Rome, the theological debate shifted to debates about Jesus, and the relationship between Jesus as God and Jesus as a human being. This produced two more splits in the church--the Nestorian movement, which date back to 431 after the Council of Ephesus, and the Monophysite churches which split with the others in 451, after the Council of Chalcedon.