Heresy as generally defined as a departure from the traditional Christian beliefs; the creation of new ideas, rituals and forms of worship within the Christian church. The heretics were branded not only as enemies of the church but also as enemies of the state. Persecution became widespread as popes authorized inquisitions. Those investigations often resulted in torture and execution of innocent victims. Thousands of people were imprisoned and burned at the stake. Most heresy proposes views of Jesus Christ and God that are contrary to what is found in the Bible.

A religious doctrine or system of doctrines proclaimed by ecclesiastical authority as true. Christianity inherited the formative dogmas of Judaism but reinterpreted them in light of the view that Jesus was and is the messiah. When early Christianity became influenced by Hellenism the concept of dogma became more important to the early church.

A doctrine or a corpus of doctrines relating to matters such as morality and faith, set forth in an authoritative manner by a church.

Arianism can be traced back to certain early doctrines which overemphasized the oneness of God, to the extent of obliterating the distinction of persons in the Blessed Trinity or of 'subordinating' the Son to the Father, making him inferior to the Father.

The main differences with Christianity and gnostic belief were that god, who was purely good, could not have created the world, as the world contained evil. Hence gnosticism created a mythology much like Greek mythology in which numerous other forces were the children of god. These children in turn created our world. One such child was Christ who descended to earth to share his knowledge, some secret knowledge of which the gnostics claimed to be only part of their religion (the unwritten, verbal knowledge passed on by Christ). Also associated with gnosticism are the beliefs that all matter was evil, including the human body and that Christs' divine spirit only descended into the man Jesus with his baptism and left him before his crucifiction, leaving the man, not the Messiah to suffer on the cross.

Modalism is probably the most common theological error concerning the nature of God. It is a denial of the Trinity. Modalism states that God is a single person who, throughout biblical history, has revealed Himself in three modes, or forms. God is a single person who first manifested himself in the mode of the Father in Old Testament times. At the incarnation, the mode was the Son and after Jesus' ascension, the mode is the Holy Spirit. These modes are consecutive and never simultaneous. This view states that the Father, the Son, and the Holy Spirit never all exist at the same time, only one after another. Modalism denies the distinctiveness of the three persons in the Trinity even though it retains the divinity of Christ.

Marcionism was an Early Christian dualist belief system that originated in the teachings of Marcion of Sinope at Rome. Marcion believed Jesus Christ was the savior sent by God and Paul of Tarsus was his chief apostle, but he rejected the Hebrew Bible and the God of Israel. Marcionists believed that the wrathful Hebrew God was a separate and lower entity than the all-forgiving God of the New Testament. This belief was in some ways similar to Gnostic Christian theology; notably, both are dualistic. Marcionism was denounced by its opponents as heresy, and written against, notably by Tertullian, in a five-book treatise Adversus Marcionem

The Novatianists were early Christians following Antipope Novatian, held a strict view that refused readmission to communion of Lapsi, those baptized Christians who had denied their faith or performed the formalities of a ritual sacrifice to the pagan gods, under the pressures of the persecution sanctioned by Emperor Decius, in AD 250. They were declared heretical.

It is a doctrine in Christian theology which holds that God the Son and God the Holy Spirit are eternally subordinate to God the Father, implying a hierarchical view of the Trinity. Subordinationism is sometimes mistakenly confused with Arianism. While Arius and his followers were certainly also subordinationist, the Arians also went further to assert that there was a time when Christ did not. In many Christian theological circles, subordinationism is treated as heresy. In other circles, subordinationism is seen as biblical middle ground between extremes of Modalism and Unitarianism.

Montanism is named after its founder Montanus, though the movement is also known as the Phrygians. The sect was founded in about156 AD by Montanus in Phrygia. The movement was a response to what Montanus saw as the relaxation in Christian zeal by the church itself. All his followers, not merely the priests, were discouraged from marriage. Second marriages were absolutely forbidden. Martyrdom was invited, any followers who declined a chance of martyrdom was condemned. Also harsh regimes of fasting were followed. The sect also was convinced that the end of the world was imminent and that Christ was to return in the immediate future. The movement continued until the sixth century when emperor Justinian vehemently suppressed it. Loyal to their creed, as well as fanatical, the montanists of Constantinople rather committed suicide than surrender. They gathered in their churches and then set light to them, perishing in the flames.

An early Christian belief which maintained that apostate priests were incapable of administering the sacraments, as opposed to the orthodox view that any sacrament administered by a properly ordained priest or bishop is valid, regardless of how sinful he is or if he has converted to another religion. Donatism was the error taught by Donatus, bishop of Casae Nigrae that the effectiveness of the sacraments depends on the moral character of the minister.

Nestorianism claimed that Jesus was host to two separate persons, that of the son of god and that of a mortal man. It was as such a direct response to Apollinarianism. In an attempt to dispell arianism, disputed the description of 'Mother of God' for Mary. Namely because this title indicated that, if Christ was born of her, he had to be younger than her. As he was eternal as god, Mary could only be the mother of Jesus, the man. It is said that Theodore of Mopsuestia was most likely the first nestorian. Although it only came to prominence after his death and under his pupil Nestorius who gave name to the heresy. Nestorianism though proved a success to the east of the Roman empire. Missions were opened in neighbouring regions such as Persia as well as far away places such as India and perhaps even China.

It is also known as Eutychianism named after its founder Eutyches. Eutyches openly disagreed with the definition of the Christian creed of AD 433 in its condemnation of Nestorianism. He believed that it was a compromise with that heresy and hence that the church was guilty of Nestorianism itself. He developed a creed of his own which claimed that Christ did not possess two natures (divine and human), but that Christ was of two natures. In his view Christ had merged the two natures into one.

Pelagianism concerned itself with man. Pelagius is a monk from Britain. He gave rise to the heresy. He came to Rome in about AD 390 where he should meet the laywer Coeletius and Julian, the Bishop of Eclanum in Campania. Together these three men become the figure heads of the Pelagian heresy. In their view every child was born absolutely innocent, free of what the traditional church called 'the original sin'. In effect this menat that to Pelagius Christ was not a saviour who took Adam's original sin upon himself, but merely a teacher who gave mankind an example of what man should be. Man could, by discipline and will- power alone leed a righteous life, without the help of god. Pelagius insisted man needed not god's grace, but could act on his own behalf, for good as well as evil.

Monothelitism was an attempt to mend the gap between the Chalcedonian and Monophysite understandings of the nature of Christ. This conflict had been going on since the first half of the 5th century, when the Monothelite definition was introduced early in the 7th century. Monothelitism avoided the apparently unsolvable question of whether Christ had two natures, one human and one divine, or only one nature. Rather it placed the focus on stating that the nature had only one will and one operation, although, still Christ was defined to have two natures. the compromise intended to give the Monophysites the one will, while the Chalcedonians would keep their dual nature. The idea would cause much interest, it was approved by both the Patriarch of Alexandria and the Pope of Rome. But quickly the controversy would show itself, and Monothelitism would never become a success. It was largely because it did not solve any conflicts, it simply introduced more to disagree upon.