The Sethians were one of the main currents of Gnosticism during the 2nd and 3rd century CE, alongside with Valentinianism. It originated in the second-century CE as a fusion of two distinct Hellenistic Judaic, and was influenced by Christianity and Middle Platonism.
The Sethians (Latin Sethoitae) are first mentioned, alongside the Ophites, in the 2nd century, by Irenaeus and in Pseudo-Tertullian (Ch.30). According to Frederik Wisse all subsequent accounts appear to be largely dependent on Irenaeus. Hippolytus repeats information from Irenaeus.
According to Epiphanius of Salamis (c.375) Sethians were in his time found only in Egypt and Palestine, although fifty years before they had been found as far away as Greater Armenia.
Philaster's (4th centruy CE) Catalogue of heresies places the Ophites, Cainites, and Sethians as pre-Christian Jewish sects. However, since Sethians identified Seth with Christ (Second Logos of the Great Seth), Philaster's belief that the Sethians had pre-Christian origins, other than in syncretic absorption of Jewish and Greek pre-Christian sources, has not found acceptance in later scholarship.
According to John D. Turner, British and French scholarship tends to see Sethianism as "a form of heterodox Christian speculation," while German And American scholarship views it as "a distinctly inner-Jewish, albeit syncretistic and heterodox, phenomenon." Roelof van den Broek notes that "Sethianism" may never have been a separate religious movement, but that the term rather refers to a set of mythological themes which occur in various texts. According to Turner, Sethianism was influenced by Christianity and Middle Platonism, and six phases can be discerned in the interation of Sethianism with Christianity and Platonism.
Phase 1. According to Turner, two different groups, existing before the second century CE, formed the basis for the Sethians: a Jewish group of possibly priestly lineage, the socalled Barbeloites, named after Barbelo, the first emanation of the Highest God, and a group of Bibilical exegetes, the Sethites, the "seed of Seth."