St. Irenaeus, Bishop of Lyons, describes several schools of Gnosticism which were prevalent among pre-Nicene Christianity. He then refutes these beliefs as heresies by contrasting them with what he describes as catholic, orthodox Christianity. Against Heresies demonstrates that earliest Christianity was a fascinating and diverse plethora of beliefs, debates, and schisms.

Eusebius in his Ecclesiastical History tells us that in addition to his great work Against Heresies, St Irenaeus wrote A Discourse in Demonstration of the Apostolic Preaching. This work was entirely lost sight of: no one seems ever to have quoted a word of it. But it has quite recently reappeared in an Armenian manuscript together with Books IV and V of the greater work. The Armenian translation proves to be a fairly close rendering of the original Greek… What Irenaeus undertakes in the present...