Christian denominations established in the 3rd century

Arianism () is a Christological doctrine that rejects the traditional notion of the Trinity, teaching that Jesus was created by God and is therefore distinct from God. It is named after its proponent Arius (250 or 256 – 336 AD) and is regarded as heretical by most modern mainstream branches of Christianity. Arianism is held by a minority of modern denominations, although some of these groups espouse related doctrines such as Socinianism, and others avoid the term "Arian" because of its historically negative connotations. Modern denominations sometimes associated with the teaching include Jehov

The Elcesaites, Elkasaites, Elkesaites or Elchasaites were an ancient Jewish Christian sect in Lower Mesopotamia, then the province of Asoristan in the Sasanian Empire that was active between the early second century and the fifth century CE. The members of this sect, which originated in the Transjordan, performed frequent baptisms for purification and had a Gnostic orientation.

Novatianism or Novationism was an early Christian sect devoted to the theologian Novatian () that 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). The Church of Rome declared the Novatianists heretical following the letters of Saint Cyprian of Carthage and Ambrose wrote against them. Novatianism survived until the 8th century.

Christianity as practiced by the ancient Goths