Discovered in 1945 near the village of Nag Hammadi in Upper Egypt, they are fourth-century papyrus manuscripts that formed part of a gnostic library. The writings are a valuable source of information about gnostic beliefs and practices. From them we can see more clearly the arguments and the theology the gnostics used in their attacks on the Catholic Church.
Although some writings are fragmentary, enough are still intact that a fairly clear picture of gnosticism emerges in the pseudo-gospels and epistles. Included in the Nag Hammadi collection are such spurious works as the Apocryphon of John, the Gospel of Philip, the Apocalypse of Paul, and the Gospel of Mary.
Scholars were delighted to discover several works whose existence was known in the early centuries of the Church but which were presumed lost. Perhaps the best treatment in English of these writings is The Nag Hammadi Library (San Francisco: Harper & Row, 1988).
Many Catholic theologians of the first several centuries devoted themselves to refuting the gnostic arguments, in particular, Irenaeus of Lyons (140-202), who wrote a devastating critique of gnosticism in his masterful five-volume work, Detection and Overthrow of the Gnosis Falsely So-Called, more commonly known as Against Heresies.