Cerdo, the gnostic teacher of the middle of the 2nd c., and placed by Theodoretus (Hær. Fab. i. 24) in the reign of Antoninus, a.d. 138–161, is described by the Ps. Tertullian as denying that Christ came in the substance of the flesh, but in appearance only. According to Marcion the greater follower of Cerdo, Christ was not born at all, but came down from heaven to Capernaum a.d. 29, his body being an appearance and his death an illusion. Simon Magus, the “father of all heretics” of Irenæus (adv. Hær. pr. in lib. iii.) is apparently quoted rather as the supposed originator of Gnosticism, than from any definite knowledge of his tenets.