Callixtus—opposed as in other matters, by the schismatic Hippolytus—favors a policy of readmitting adulterers, apostates, and murderers to communion.

Hippolytus, an ethical conservative, is scandalized when Callixtus extends absolution to Christians who had committed grave sins, such as adultery.

At this time, he seems to have allowed himself to be elected as a rival Bishop of Rome Sabellius, a Christian priest, denies the Christian doctrine of the Trinity, contending that God is three only in relation to the world, in so many "manifestations" or "modes" of divine activity.

Sabellius teaches that the unity and identity of God are such that the Son of God did not exist before the incarnation.

Further, because the Father and the Son are thus one, Sabellius expresses the view (called Patripassionism) that the Father suffered with the Son in his passion and death.

Callistus and Hippolytus both oppose the Sabellianist heresy, as do Tertullian and Dionysius of Alexandria.

In order to affirm the unity of God and guard against the charge of polytheism, Tertullian coins the theological term “Monarchianism” to describe this and other forms of the popular second- and third-century heresies that reject Trinitarianism.

Tertullian defines Sabellianism and Patripassionism as the Modalistic form of Monarchism, which maintains God the Father's incarnation in order to hold the Son's divinity and the unity of God.

The other form, called Adoptionist, or Dynamic, views Jesus as a unique person, divinely energized, called to be the Son of God.

Both heresies represent an attempt to reconcile the doctrines of the incarnation and Trinity with philosophical concepts of the unity and immateriality of God.

Callistus, in condemning Sabellius, aids in the establishment and codification of church doctrine about the nature of the Trinity.

It is possible that Callixtus was martyred around 222, perhaps during a popular uprising, but the legend that he was thrown down a well has no historical foundation.

Urban succeeds him.

The charismatic Christian Platonist Origen has spent the period from 218 to 230 in Alexandria, where he has produced a great body of writings, among them the Hexapla, the first attempt to establish a critical text of the Old Testament; his commentaries on Matthew and John, which establish him as the Christian church’s first important biblical scholar; the De Principiis (or Peri Archon), a dogmatic treatise on God and the world; and the Contra Celsum, in which he refutes paganism.

Dionysius of Alexandria, a renowned young theologian, mounts a vigorous opposition to the Sabellianist heresy, denying the reality of the three persons of the Trinity.

His detractors accuse him of tritheism, belief in three gods.

Origen, on a return visit to Palestine in 230, is ordained a priest by the bishops of Jerusalem and Caesarea, whereupon Demetrius, bishop of Alexandria, excommunicates him, strips him of his priesthood, and orders him into exile.

Dionysius of Alexandria, born to a wealthy pagan family here, has spent most of his life reading books and carefully studying the traditions of heretics.

After having converted to Christianity at a mature age, he had joined the Catechetical School of Alexandria and been a student of Origen and Heraclas.

Dionysius later became leader of the school and presbyter of the Christian church, in 231 succeeding Heraclas.

He had in 248 succeeded the deceased Heraclas as Bishop of Alexandria.

Dionysius in his later writings describes the period during which the city of Alexandria is subject to the legal persecution instituted by Decius against Christians.

The many extreme horrors faced by Alexandrians during the persecution had included death by stoning, the gouging of eyes, and being dragged through the streets as well as being burnt alive.

Dionysius himself had been captured during the persecution, but was later freed by a mob of Christian passersby and fled into the desert.