1st–2nd c.

Gnosticism as the chief threat to the Church in the 2nd century

Gnosticism was not a single movement but a broad syncretic current of the first and second centuries that combined Jewish elements, Christian teachings and Eastern philosophy. It was active in Syria, Asia Minor, Egypt, Rome and Gaul. The books place the beginnings of the movement in the apostolic age (Cerinthus) and its developed form at the start of the second century.

The schools of Cerinthus, Saturninus, Valentinus (whose pupils included Ptolemy and Heracleon) and Basilides are known. Gnostic views provoked sharp polemic from Ignatius, and then from Irenaeus of Lyons and Clement of Alexandria. Related Jewish-Christian movements included the Ebionites, Nazarenes and Elkesaites.

In opposition to Gnosticism the Church for the first time worked out the "rule of faith" and began to define the canon of the New Testament.