St. Irenaeus, the bishop of Lyon, France, wrote Against Heresies in 180 AD. It is a collected work made up of five books, in which Irenaeus examines the many schools of Gnostic thought of his day, in addition to various heretical Christian sects. He contrasts these with the orthodoxy of Christianity. This version of the work contains the first three books, which, before the discovery of the Nag Hammadi Library, were the best surviving description of Gnosticism. The early authorship of the document gives a rare window into the doctrine of the early church, and what scriptures were considered genuine.